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Hong Nhan Nong, Lorenz J. Falling, Arno Bergmann, Malte Klingenhof, Hoang Phi Tran, Camillo Spöri, Rik Mom, Janis Timoshenko, Guido Zichittella, Axel Knop-Gericke, Simone Piccinin, Javier Pérez-Ramírez, Beatriz Roldan Cuenya, Robert Schlögl, Peter Strasser, Detre Teschner & Travis E. Jones

Key role of chemistry versus bias in electrocatalytic oxygen evolution

Nature 2020, 587, 408-413

DOI: 10.1038/s41586-020-2908-2


The oxygen evolution reaction has an important role in many alternative-energy schemes because it supplies the protons and electrons required for converting renewable electricity into chemical fuels. Electrocatalysts accelerate the reaction by facilitating the required electron transfer, as well as the formation and rupture of chemical bonds. This involvement in fundamentally different processes results in complex electrochemical kinetics that can be challenging to understand and control, and that typically depends exponentially on overpotential. Such behaviour emerges when the applied bias drives the reaction in line with the phenomenological Butler–Volmer theory, which focuses on electron transfer, enabling the use of Tafel analysis to gain mechanistic insight under quasi-equilibrium or steady-state assumptions. However, the charging of catalyst surfaces under bias also affects bond formation and rupture, the effect of which on the electrocatalytic rate is not accounted for by the phenomenological Tafel analysis and is often unknown. Here we report pulse voltammetry and operando X-ray absorption spectroscopy measurements on iridium oxide to show that the applied bias does not act directly on the reaction coordinate, but affects the electrocatalytically generated current through charge accumulation in the catalyst. We find that the activation free energy decreases linearly with the amount of oxidative charge stored, and show that this relationship underlies electrocatalytic performance and can be evaluated using measurement and computation. We anticipate that these findings and our methodology will help to better understand other electrocatalytic materials and design systems with improved performance.
René Sachse, Mika Pflüger, Juan-Jesús Velasco-Vélez, Mario Sahre, Jörg Radnik, Michael Bernicke, Denis Bernsmeier, Vasile-Dan Hodoroaba, Michael Krumrey, Peter Strasser, Ralph Kraehnert, Andreas Hertwig

Assessing Optical and Electrical Properties of Highly Active IrOx Catalysts for the Electrochemical Oxygen Evolution Reaction via Spectroscopic Ellipsometry

ACS Catal., 10, 13058-13074

DOI: 10.1021/acscatal.0c03800


Efficient water electrolysis requires highly active electrodes. The activity of corresponding catalytic coatings strongly depends on material properties such as film thickness, crystallinity, electrical conductivity, and chemical surface speciation. Measuring these properties with high accuracy in vacuum-free and non- destructive methods facilitates the elucidation of structure−activity relationships in realistic environments. Here, we report a novel approach to analyze the optical and electrical properties of highly active oxygen evolution reaction (OER) catalysts via spectroscopic ellipsometry (SE). Using a series of differently calcined, mesoporous, templated iridium oxide films as an example, we assess the film thickness, porosity, electrical resistivity, electron concentration, electron mobility, and interband and intraband transition energies by modeling of the optical spectra. Independently performed analyses using scanning electron microscopy, energy-dispersive X-ray spectroscopy, ellipsometric porosimetry, X-ray reflectometry, and absorption spectroscopy indicate a high accuracy of the deduced material properties. A comparison of the derived analytical data from SE, resonant photoemission spectroscopy, X-ray absorption spectroscopy, and X-ray photoelectron spectroscopy with activity measurements of the OER suggests that the intrinsic activity of iridium oxides scales with a shift of the Ir 5d t2g sub-level and an increase of p−d interband transition energies caused by a transition of μ1-OH to μ3-O species.
Sara E. Renfrew, David E. Starr, and Peter Strasser

Electrochemical Approaches toward CO2 Capture and Concentration

ACS Catal. 2020, 10, 13058−13074



Carbon capture and concentration of low partial pressure CO2 in air and flue gas is a key step in carbon abatement strategies. Traditional CO2 capture methods employ temperature or pressure swings; however, electrochemical swings, in which an applied potential modulates nucleophilicity, are also possible to mediate the capture and release of CO2. In contrast to the breadth of electrochemical CO2 reduction research, electrochemically mediated CO2 capture and concentration is an emerging field. Although some aspects are reminiscent of those in CO2 reduction, like local pH gradients and (bi)carbonate equilibria, ultimately electrochemical CO2 capture and concentration poses its own unique challenges that will benefit from insights from intercalative batteries, redox flow batteries, and biomimetic/-inspired design, among other fields. After an introduction to carbon capture and current chemical strategies, this Review highlights promising emerging electrochemical methods to enable CO2 capture and concentration; specifically discussed are organic redox, transition metal redox, and pH swings. It closes with an outlook and discussion of future research challenges for electrochemically mediated capture.
Henrike  Schmies,  Arno  Bergmann,  Elisabeth  Hornberger,  Jakub  Drnec,  Guanxiong Wang,  Fabio  Dionigi,  Stefanie  Kühl,  Daniel  J.S.  Sandbeck,  Karl  J.J.  Mayrhofer,  Vijay Ramani, Serhiy Cherevko, Peter Strasser

Anisotropy of Pt Nanoparticles on Carbon- and Oxide-Support and Their Structural Response to Electrochemical Oxidation Probed by in situ Techniques

Physical Chemistry Chemical Physics, 22, 22260



Identifying the structural response of nanoparticle-support ensembles to the reaction conditions is essential to determine their structure in the catalytically-active state as well as to unravel possible degradation pathways. In this work, we investigate the (electronic) structure of carbon- and oxide-supported Pt nanoparticles during electrochemical oxidation by in situ X-ray diffraction, absorption spectroscopy as well as the Pt dissolution rate by in situ mass spectrometry. We prepared ellipsoidal Pt nanoparticles by impregnation of carbon and titanium-based oxide support as well as spherical Pt nanoparticles on an indium-based oxide support by a surfactant-assisted synthesis route. During electrochemical oxidation, we show that the oxide-supported Pt nanoparticles resist (bulk) oxide formation and Pt dissolution. The lattice of smaller Pt nanoparticles exhibits a size-induced lattice contraction in the as-prepared state with respect to bulk Pt but it expands reversibly during electrochemical oxidation. This expansion is suppressed for the Pt nanoparticles with bulk-like relaxed lattice. We could correlate the formation of d-band vacancies in the metallic Pt with the Pt lattice expansion. The PtOx formation is strongest for platelet-like nanoparticles and we explain this with a higher fraction of exposed Pt(100) facets. Of all investigated nanoparticle-support ensembles, the structural response of RuO2/TiO2-supported Pt nanoparticles is the most promising with respect to their morphological and structural integrity under electrochemical reaction conditions.
Kai Zeng, Xiangjun Zheng, Cong Li, Jin Yan, Jing-Hua Tian, Chao Jin, Peter Strasser, and Ruizhi Yang

Recent Advances in Non-Noble Bifunctional Oxygen Electrocatalysts toward Large-Scale Production

Advanced Functional Materials, 2020



The oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are crucial reactions in energy conversion and storage systems including fuel cells, metal–air batteries, and electrolyzers. Developing low‐cost, high‐efficiency, and durable non‐noble bifunctional oxygen electrocatalysts is the key to the commercialization of these devices. Here, based on an in‐depth understanding of ORR/OER reaction mechanisms, recent advances in the development of non‐noble electrocatalysts for ORR/OER are reviewed. In particular, rational design for enhancing the activity and stability and scalable synthesis toward the large‐scale production of bifunctional electrocatalysts are highlighted. Prospects and future challenges in the field of oxygen electrocatalysis are presented.
Seongkoo Kang, Kyle G. Reeves, Toshinari Koketsu, Jiwei Ma, Olaf J. Borkiewicz, Peter Strasser, Alexandre Ponrouch, and Damien Dambournet

Multivalent Mg2+, Zn2+ and Ca2+ Ion Intercalation Chemistry in a Disordered Layered Structure

ACS Appl. Energy Mater. 2020



The development of practical multivalent-ion batteries critically depends on the identification of suitable positive electrode materials. To gain a better understanding of the intercalation chemistry of multivalent ions, model frameworks can be used to study the distinct specificities of possible multivalent ions, thus expanding our knowledge on the emerging “Beyond Li battery” technology. Here, we compare the intercalation chemistry of Mg2+, Zn2+ and Ca2+ ions into a disordered layered-type structure featuring water interlayers and cationic vacancies as possible host sites. The thermodynamics of cation-inserted reactions performed on the model structure indicated that these reactions are thermodynamically favourable with Zn2+ being the least stable ion. Galvanostatic measurements confirmed that the structure is inactive toward Zn2+ intercala-tion while Mg2+ can be reversibly inserted (0.37 Mg2+ per formula unit) with minor changes of the atomic arrangement as demonstrated by pair distribution function analysis. Moreover, we demonstrate that non-solvated Mg2+ was intercalated in the structure. Finally, the intercalation of Ca2+ performed at 100 °C with Ca(BF4)2 in propylene carbonate, induced the col-lapse of the layered structure releasing water molecules that contribute to the degradation of the electrolyte as revealed by the presence of CaF2 at the electrode level. The decomposition of the structure led to the formation of an electrochemically active phase featuring strong long-range disorder, yet short-range order close to that found in perovskite structures, particu-larly with corner-shared TiO6 octahedra. We, hence, hypothesize that defective CaTiO3-based perovskite could be explored as viable cathode materials for rechargeable Ca-based batteries.
Friedemann Hegge, Florian Lombeck, Edgar Cruz Ortiz, Luca Bohn, Miriam von Holst, Matthias Kroschel, Jessica Hübner, Matthias Breitwieser, Peter Strasser, and Severin Vierrath

Efficient and stable low iridium-loaded anodes for PEM water electrolysis made possible by nanofiber interlayers

ACS Appl. Energy Mater.,2020



Significant reduction of the precious metal catalyst loading is one of the key challenges for the commercialization of proton-exchange membrane water electrolyzers. In this work we combine IrOx nanofibers with a conventional nanoparticle-based IrOx anode catalyst layer. With this hybrid design we are able to reduce the iridium loading by more than 80 % while maintaining performance. In spite of an ultra-low overall catalyst loading of 0.2 mgIr/cm², a cell with a hybrid layer shows similar performance compared to a state-of-the-art cell with a catalyst loading of 1.2 mgIr/cm² and clearly outperforms identically loaded reference cells with pure IrOx nanoparticle and pure nanofiber anodes. The improved performance is attributed to a combination of good electric contact and high porosity of the IrOx nanofibers with high surface area of the IrOx nanoparticles. Besides the improved performance, the hybrid layer also shows better stability in a potential cycling and a 150h constant current test compared to an identically loaded nanoparticle reference.
Robert Marić, Christian Gebauer, Markus Nesselberger, Frédéric Hasché and Peter Strasser

Towards a Harmonized Accelerated Stress Test Protocol for Fuel Starvation Induced Cell Reversal Events in PEM Fuel Cells: The Effect of Pulse Duration

J. Electrochem. Soc., 167, 124520



Global  fuel  starvation  is  an  undesired  event  during  fuel  cell  operation  that  results  in  serious degradations  at  the  anode  catalyst  layer  caused  by  the  concomitant  reversal  of  the  cell potentials.  Several  groups  have  therefore  intensified  their  research  efforts  towards  the implementation  of  suitable  diagnostic  tools  and  accelerated  stress  test  (AST)  protocols  that mimic  cell  reversal  events.  However,  the  current  number  of  different  test  protocols  requires consolidation and harmonization to define durability targets towards cell reversal tolerance and to  benchmark  newly  developed  materials.  To  create  a  basis  for  harmonization,  this  study examines the difference between pulsed and quasi-continuous AST protocols at the catalyst-coated  membrane  level.  Utilizing  a  single-cell  setup  combined  with  an  on-line  mass spectrometer,  a  2.5-fold  increase  in  the  carbon  corrosion  rates  were  found  for  short-pulsed compared to long-lasting cell reversal events. The enhanced corrosion was associated with a 2.2-fold  higher  loss  of  electrochemically  active  surface  area  and  a  15  %  higher  reduction  in anode catalyst layer thickness. By contrast, the overall cell performance decreased additionally by 40–50 mV for samples under long-lasting cell reversal events. The decay is mainly driven by  an  increased  ohmic  resistance,  presumably  originating  from a  more  pronounced  surface oxide formation on the carbon support.
Xiangjun Zheng, Xuecheng Cao, Zhihui Sun, Kai Zeng, Jin Yan, Peter Strasser, Xin Chen, Shuhui Sun, Ruizhi Yang

Indiscrete metal/metal-N-C synergic active sites for efficient and durableoxygen electrocatalysis toward advanced Zn-air batteries

Applied Catalysis B: Environmental, 272, 118967



Carbon has been deemed promising electrocatalyst for oxygen reduction/evolution reaction (ORR/OER). However, most carbon materials are not stable in highly oxidative OER environments. Herein, nitrogen (N) and transition metal (TM) co-doped carbon nanosheets hybridizing with transition metal (TM/TM-N-C, TM = Fe, Co, Ni) are developed from biomass lysine by employing a NaCl template and molten-salt-promoted graphitization process. Among the as-synthesized TM/TM-N-C, the Ni/Ni-N-C with Ni nanocubes embedded in carbon demonstrates an excellent ORR-OER stability during the potential of 0.06–1.96 V. The rechargeable Zn-air battery with the fabricated Ni/Ni-N-C as the cathode catalyst produces a low voltage gap of 0.773 V, which is only slightly increased by 5 % after 150 cycles testing. Combined experimental and theoretical studies reveal that the exceptional activity and ORR-OER wide potential durability of Ni/Ni-N-C can be ascribed to highly active Ni-N4-C configuration, synergistic effect between Ni and Ni-N4-C, carbon nanosheets structure and formation of stable Ni3+-N for protecting carbon from oxidation.
Tim Möller, Fabian Scholten, Trung Ngo Thanh, Ilya Sinev, Janis Timoshenko, Xingli Wang, Zarko Jovanov, Manuel Gliech, Beatriz Roldan Cuenya, Ana Sofia Varela, and Peter Strasser

Electrocatalytic CO2 Reduction on CuOx Nanocubes: Tracking the Evolution of Chemical State, Geometric Structure, and Catalytic Selectivity using Operando Spectroscopy
Angewandte Chemie, 132, 2-12



The direct electrochemical conversion of carbon dioxide (CO2) into multi‐carbon (C2+) products still faces fundamental and technological challenges. While facet‐controlled and oxide‐derived Cu materials have been touted as promising catalysts, their stability has remained problematic and poorly understood. The present work uncovers changes in the chemical and morphological state of supported and unsupported Cu2O nanocubes during operation in low‐current H‐Cells and in high‐current Gas Diffusion Electrodes (GDEs) using neutral pH buffer conditions. While unsupported nanocubes achieved a sustained C2+ faradaic efficiency of around 60% for 40h, the dispersion on a carbon support sharply shifted the selectivity pattern towards C1 products. Operando XAS and time‐resolved electron microscopy revealed the degradation of the cubic shape and, in the presence of a carbon support, the formation of small Cu‐seeds during the surprisingly slow reduction of bulk Cu2O. Here, the initially (100)‐rich facet structure has presumably no controlling role on the catalytic selectivity, whereas the oxide‐derived generation of under‐coordinated lattice defects, as revealed by the operando Cu‐Cu coordination numbers, can support the high C2+ product yields.
Woong Hee Lee, Jaekyung Yi, Hong Nhan Nong, Peter Strasser, Keun Hwa Chae, Byoung Koun Min, Yun Jeong Hwang, and Hyung-Suk Oh

Electroactivation-induced IrNi Nanoparticles under Different pH Conditions for Neutral Water Oxidation

Nanoscale, 12, 14903-14910



The electrochemical oxidation processes can affect electronic structure and activate catalytic performance of preciousmetal and transition-metal based catalysts for oxygen evolution reaction (OER). Also there are emerging requirements to develop OER electrocatalysts in various pH condition in order to couple with different reduction reactions. Herein, we studied the pH effect on electroativation of IrNi alloy nanoparticles supported on carbon (IrNi/C) and the activated IrNiOx/C evaluated the electrocatalytic activities for water oxidation in a neutral condition. In addition, their electronic structures and atomic arrangement were analyzed in-situ/operando X-ray absorption spectroscopy (XAS) and identical location transmission electron microscopy technique showing reconstruction of the metal elements during electroactivation due to their different stabilities depending on the electrolyte pH. IrNiOx/C activated under neutral pH conditions showed a mildly oxidized thin IrOx shell. Meanwhile, IrNiOx/C activated in acidic and alkaline electrolytes showed Ni-leached IrOx and Ni-rich IrNiOx surfaces, respectively. Especially, the surface of IrNiOx/C activated in alkaline condition shows IrOx with high d-band hole and NiOx with high oxidation state leading excellent OER catalytic activity in neutral media (η = 384 mV at 10 mA cm–2) where much lower OER activity was reported compared with alkaline or acid condition. Our results, which showed that electrochemically activated catalysts under different pH conditions exhibit a unique electronic structure by modifying the initial alloy catalyst, can be applied for the design of catalysts suitable for various electrochemical reactions.
Fabio Dionigi and Peter Strasser


ESRF Highlights 2019, 147



Octahedral PtNi nanoparticles are promising catalysts for the oxygen reduction reaction in fuel cell applications. The structural changes associated with Ni leaching during operation have been investigated by in-situ wide-angle X-ray  scattering  (WAXS).  Atomic  Ni  losses,  correlating  to  expansion  of  the  crystal  lattice  parameters,  largely affect the activity.
Toshinari Koketsu, Jiwei Ma, Benjamin.J. Morgan, Monique Body, Christophe Legein,Pooja Goddard, Olaf J. Borkiewicz, Peter Strasser, Damien Dambournet

Exploiting Cationic Vacancies for Increased Energy Densities in Dual-Ion Batteries

Energy Storage Materials, 25, 154-163



Dual-ion Li–Mg batteries offer a potential route to cells that combine desirable properties of both single-ion species. To maximize the energy density of a dual-ion battery, we propose a strategy for achieving simultaneous intercalation of both ionic species, by chemically modifying the intercalation host material to produce a second, complementary, class of insertion sites. We show that donor-doping of anatase TiO2 to form large numbers of cationic vacancies allows the complementary insertion of Li+ and Mg2+ in a dual-ion cell with a net increase in cell energy density, due to a combination of an increased reversible capacity, an increased operating voltage, and a reduced polarization. By tuning the lithium concentration in the electrolyte, we achieve full utilization of the Ti4+/Ti3+ redox couple with excellent cyclability and rate capability. We conclude that native interstitial sites preferentially accommodate Li+ ions, while Mg2+ ions occupy single-vacancy sites. We also predict a narrow range of electrochemical conditions where adjacent vacancy pairs preferentially accommodate one ion of each species, i.e., a [LiTi ​+ ​MgTi] configuration. These results demonstrate the implementation of additional host sites such as cationic sites as an effective approach to increase the energy density in dual-ion batteries.
Hadla Ferreira, Martin Gocyla, Hadma Ferreira, Rennan Araujo, Caio Almeida, Marc Heggen, Rafal  Dunin-Borkowski, Katlin Eguiluz, Peter Strasser, and Giancarlo R. Salazar-Banda

A Comparative Study of the Catalytic Performance of Pt-Based Bi and Trimetallic Nanocatalysts Towards Methanol, Ethanol, Ethylene Glycol, and Glycerol Electro-Oxidation

J. Nanosci. Nanotechnol., 20, 10



Carbon-supported platinum is used as an anode and cathode electrocatalyst in low-temperature fuel cells fueled with low-molecular-weight alcohols in fuel cells. The cost of Pt and its low activity towards the complete oxidation of these fuels are significant barriers to the widespread use of these types of fuel cells. Here, we report on the development of PtRhNi nanocatalysts supported on carbon made using a reduction chemistry method with different atomic rates. The catalytic activity of the developed catalysts towards the electro-oxidation of methanol, ethanol, ethylene glycol, and glycerol in acidic media was studied. The obtained catalysts performances were compared with both commercial Pt/C and binary Pt75Ni25/C catalyst. The nanostructures were characterized, employing inductively coupled plasma optical emission spectrometer, X-ray diffraction, scanning transmission electron microscopy, and energy-dispersive X-ray spectroscopy. The binary catalyst presents a mean particle size of around 2 nm. Whereas the ternary catalysts present particles of similar size and with some large alloy and core–shell structures. The alcohol oxidation onset potential and the current density measured after 3600 s of chronoamperometry were used to classify the catalytic activity of the catalysts towards the oxidation of methanol, ethanol, ethylene glycol, and glycerol. The best PtRhNi/C catalyst composition (i.e., Pt43Rh43Ni14/C) presented the highest activity for alcohols oxidation compared with all catalysts studied, indicating the proper tuning composition influence in the catalytic activity. The enhanced activity of Pt43Rh43Ni14/C can be attributed to the synergic effect of trimetallic compounds, Pt, Ni, and Rh.
Fang Luo, Aaron Roy, Luca Silvioli, David A. Cullen, Andrea Zitolo, Moulay Tahar Sougrati, Ismail Can Oguz, Tzonka Mineva, Detre Teschner, Stephan Wagner, Ju Wen, Fabio Dionigi, Ulrike I. Kramm, Jan Rossmeisl, Frédéric Jaouen and Peter Strasser

P-block single-metal-site tin/nitrogen-doped carbon fuel cell cathode catalyst for oxygen reduction reaction

Nature Materials, 2020



This contribution reports the discovery and analysis of a p-block Sn-based catalyst for the electroreduction of molecular oxygen in acidic conditions at fuel cell cathodes; the catalyst is free of platinum-group metals and contains single-metal-atom actives sites coordinated by nitrogen. The prepared SnNC catalysts meet and exceed state-of-the-art FeNC catalysts in terms of intrinsic catalytic turn-over frequency and hydrogen–air fuel cell power density. The SnNC-NH3 catalysts displayed a 40–50% higher current density than FeNC-NH3 at cell voltages below 0.7 V. Additional benefits include a highly favourable selectivity for the four-electron reduction pathway and a Fenton-inactive character of Sn. A range of analytical techniques combined with density functional theory calculations indicate that stannic Sn(iv)Nx single-metal sites with moderate oxygen chemisorption properties and low pyridinic N coordination numbers act as catalytically active moieties. The superior proton-exchange membrane fuel cell performance of SnNC cathode catalysts under realistic, hydrogen–air fuel cell conditions, particularly after NH3 activation treatment, makes them a promising alternative to today’s state-of-the-art Fe-based catalysts.
Elisabeth Hornberger, Henrike Schmies, Benjamin Paul, Stefanie Kühl and Peter Strasser

Design and Validation of a Fluidized Bed Catalyst Reduction Reactor for the Synthesis of Well-Dispersed Nanoparticle Ensembles

J. Electrochem. Soc., 167, 114509



Pt-based nanoparticles supported on carbon materials are state-of-the-art electrocatalysts for proton exchange membrane fuel cells (PEMFCs). Interparticle distance and particle size of the supported nanoparticles play a crucial role for the catalyst's performance. The synthesis approach of wet impregnation and thermal reduction in a regular static packed-bed tube furnace often results in poorly distributed Pt particles in terms of interparticle distance and particle size. Here, we report on a fluidized bed gas reduction reactor for the preparation of supported well-dispersed nanoparticles. To validate the reactor, we compared and contrasted Pt nanoparticle ensembles supported on Vulcan XC 72R prepared using a conventional, horizontal static packed bed tube furnace, and using our novel vertical fluidized bed reduction reactor. The catalysts were physico-chemically characterized and electrochemically tested with respect to their electrocatalytic oxygen reduction reaction reactivity using rotating disk electrode (RDE) experiments. Our results demonstrate that the nanoparticle samples prepared in the customized fluidized bed reduction reactor showed significantly superior mono-dispersion and more homogeneously spatial distribution that resulted in improved electrochemical stability.
Yanyan Sun, Lei Han, Peter Strasser

A Comparative Perspective of Electrochemical and Photochemical Approaches for Catalytic H2O2 Production

Chemical Society Reviews, 49, 6605-6631

DOI: 10.1039/D0CS00458H


Hydrogen peroxide (H2O2) has a wide range of important applications in various fields including chemical industrial, environmental remediation, and sustainable energy conversion/storage. Nevertheless, the stark disconnect between today’s huge market demand and the historical unsustainability of the currently-used, industrial anthraquinone-based production process is promoting extensive research on the development of efficient, energy-saving and sustainable methods for H2O2 production. Among several sustainable strategies, H2O2 production via the electrochemical and photochemical routes has shown a particular appeal, because only water, O2, and solar energy/electricity are involved during the whole process. In the past few years, considerable efforts have been devoted to the development of advanced electrocatalysts and photocatalysts for an efficient and scalable H2O2 production with high efficiency and stability. In this review, we compare and contrast the two distinct, yet inherently closely linked catalytic processes, before we detail recent advances in the design, preparation, and applications of different H2O2 catalyst systems from the viewpoint of electrochemical and photochemical approach. We close with a balanced perspective on remaining future scientific and technical challenges and opportunities.
Damien Dambournet, Christophe Legein, Ben Morgan, Monique Body, Olaf Borkiewicz, Franck Fayon, vincent sarou-kanian, Jiwei Ma, Peter Strasser, Toshinari Koketsu, Wei Xiankui, Marc Heggen

Atomic Insights into Aluminium‐Ion Insertion in Defective Anatase for Batteries

Angewandte Chemie, 2020



Aluminium batteries constitute a safe and sustainable high–energy‐density electrochemical energy‐storage solution. Viable Al‐ion batteries require suitable electrode materials that can readily intercalate high‐charge Al 3+ ions. Here, we investigate the Al 3+ intercalation chemistry of anatase TiO 2 and how chemical modifications influence the accommodation of Al 3+ ions. We use fluoride‐ and hydroxide‐doping to generate high concentrations of titanium vacancies. The coexistence of these hetero‐anions and titanium vacancies leads to a complex insertion mechanism, attributed to three distinct types of host sites: native interstitials sites, single vacancy sites, and paired vacancy sites. We demonstrate that Al 3+ induces a strong local distortion within the modified TiO 2 structure, which affects the insertion properties of the neighbouring host sites. Overall, specific structural features induced by the intercalation of highly‐polarizing Al 3+ ions should be considered when designing new electrode materials for multivalent batteries.
Mathias Primbs, Yanyan Sun, Aaron Roy, Daniel Malko, Asad Mehmood, Moulay-Tahar Sougrati, Pierre-Yves Blanchard, Gaetano Granozzi, Tomasz Kosmala, Giorgia Daniel, Plamen Atanassov, Jonathan Sharman, Christian Durante, Anthony Kucernak, Deborah Jones, Frederic Jaouen and Peter Strasser

Establishing reactivity descriptors for platinum group metal (PGM)-free Fe–N–C catalysts for PEM fuel cells

Energy Environ. Sci., 2020



We report a comprehensive analysis of the catalytic oxygen reduction reaction (ORR) reactivity of four of today's most active benchmark platinum group metal-free (PGM-free) iron/nitrogen doped carbon electrocatalysts (Fe–N–Cs). Our analysis reaches far beyond previous such attempts in linking kinetic performance metrics, such as electrocatalytic mass-based and surface area-based catalytic activity with previously elusive kinetic metrics such as the active metal site density (SD) and the catalytic turnover frequency (TOF). Kinetic ORR activities, SD and TOF values were evaluated using in situ electrochemical NO2− reduction as well as an ex situ gaseous CO cryo chemisorption. Experimental ex situ and in situ Fe surface site densities displayed remarkable quantitative congruence. Plots of SD versus TOF (“reactivity maps”) are utilized as new analytical tools to deconvolute ORR reactivities and thus enabling rational catalyst developments. A microporous catalyst showed large SD values paired with low TOF, while mesoporous catalysts displayed the opposite. Trends in Fe surface site density were linked to molecular nitrogen and Fe moieties (D1 and D2 from 57Fe Mössbauer spectroscopy), from which pore locations of catalytically active D1 and D2 sites were established. This cross-laboratory analysis, its employed experimental practices and analytical methodologies are expected to serve as a widely accepted reference for future, knowledge-based research into improved PGM-free fuel cell cathode catalysts.
Woong Hee Lee, Young-Jin Ko, Yongjun Choi, Si Young Lee, Chang Hyuck Choi, Yun Jeong Hwang, Byoung Koun Min, Peter Strasser, Hyung-Suk Oh

Highly selective and scalable CO2 to CO - Electrolysis using coral-nanostructured Ag catalysts in zero-gap configuration

Nano Energy, 76, 105030



The direct electroreduction of CO2 to pure CO streams has attracted much attention for both academic research and industrial polymer synthesis development. Here, we explore catalytically very active, coral-structured Ag catalyst for the generation of pure CO from CO2-feeds in lab-bench scale zero-gap CO2 electrolyzer. Coral-shaped Ag electrodes achieved CO partial current densities of up to 312 mA cm−2, EECO of 38%, and FECO clearly above 90%. In-situ/operando X-ray Absorption Spectroscopy revealed the sustained presence of Ag+ subsurface species, whose local electronic field effects constitute likely molecular origins of the favorable experimental kinetics and selectivity. In addition, we show how electrode flooding in zero-gap CO2 electrolyzer compromises efficient CO2 mass transfer. Our studies highlight the need for a concomitant consideration of factors related to intrinsic catalytic activity of the active phase, its porous structure and its hydrophilicity/phobicity to achieve a sustained high product yield in AEM zero-gap electrolyzer.
Fabio Dionigi, Zhenhua Zeng, Ilya Sinev, Thomas Merzdorf, Siddharth Deshpande, Miguel Bernal Lopez, Sebastian Kunze, Ioannis Zegkinoglou, Hannes Sarodnik, Dingxin Fan, Arno Bergmann, Jakub Drnec, Jorge Ferreira de Araujo, Manuel Gliech, Detre Teschner, Jing Zhu,Wei-Xue Li, Jeffrey Greeley, Beatriz Roldan Cuenya and Peter Strasser

In-situ structure and catalytic mechanism of NiFe and CoFe layered double hydroxides during oxygen evolution

Nature Communications, 11, 2522



NiFe and CoFe (MFe) layered double hydroxides (LDHs) are among the most active electrocatalysts for the alkaline oxygen evolution reaction (OER). Herein, we combine electrochemical measurements, operando X-ray scattering and absorption spectroscopy, and density functional theory (DFT) calculations to elucidate the catalytically active phase, reaction center and the OER mechanism. We provide the first direct atomic-scale evidence that, under applied anodic potentials, MFe LDHs oxidize from as-prepared α-phases to activated γ-phases. The OER-active γ-phases are characterized by about 8% contraction of the lattice spacing and switching of the intercalated ions. DFT calculations reveal that the OER proceeds via a Mars van Krevelen mechanism. The flexible electronic structure of the surface Fe sites, and their synergy with nearest-neighbor M sites through formation of O-bridged Fe-M reaction centers, stabilize OER intermediates that are unfavorable on pure M-M centers and single Fe sites, fundamentally accounting for the high catalytic activity of MFe LDHs.
Sören Dresp,   Trung Ngo Thanh,   Malte Klingenhof,   Sven Brueckner,   Philipp Hauke  and  Peter Strasser  

Efficient direct seawater electrolysers using selective alkaline NiFe-LDH as OER catalyst in asymmetric electrolyte feeds

Energy Environ. Sci., 13, 1725-1729



Direct seawater electrolysis faces fundamental catalytic and process engineering challenges. Here we demonstrate a promising seawater electrolyser process using asymmetric electrolyte feeds.
We further investigated the faradaic O2 efficiency of NiFe-LDH in alkalinized Cl-containing electrolytes in comparison to commercial IrOx-based catalysts. Other than IrOx, NiFe-LDH prevents the
oxidation of Cl and appears highly selective for the oxygen evolution reaction in alkalinized seawater even at cell potentials beyond 3.0 Vcell.
Woong Hee Lee, Hong Nhan Nong, Chang Hyuck Choi, Keun Hwa Chae, Yun Jeong Hwang, Byoung Koun Mina, Peter Strasser and Hyung-Suk Oh

Carbon-Supported IrCoOx nanoparticles as an efficient and stable OER electrocatalyst for practicable CO2 electrolysis

Applied Catalysis B: Environmental, 269, 118820



The development of an efficient and stable oxygen evolution reaction (OER) electrocatalyst operating under pH-neutral conditions is vital for the realization of sustainable CO2 reduction reaction (CO2RR) systems in the future. For commercializing this system, it is also important to be able to use general-purpose water as an electrolyte. Here, we explore, characterize and validate a new IrCoOx mixed metal oxide as efficient and stable OER catalyst, before we investigate and proof its suitability as counter electrode to a CO2RR cathode operating under pH-neutral conditions. More specifically, carbon-supported IrCoOx core-shell nanoparticles exhibited a highly efficient OER catalytic activity and stability compared to state-of-art reference IrOx catalysts in CO2-saturated 0.5 M KHCO3 tap-water. IrCoOx/C also exhibited a significantly improved electrochemical oxidation and corrosion resistance than IrOx, resulting in a beneficial suppression of Ir dissolution. The application of IrCoOx/C in the CO2 electrolyzer displayed superior CO space-time yields over prolonged electrolyzer tests.
Manuel Gliech, Mikaela Görlin, Martin Gocyla, Malte Klingenhof, Arno Bergmann, Sören Selve, Camillo Spöri, Marc Heggen, Rafal E. Dunin-Borkowski, Jin Suntivich and Peter Strasser

Solute Incorporation at Oxide–Oxide Interfaces Explains How Ternary Mixed‐Metal Oxide Nanocrystals Support Element‐Specific Anisotropic Growth

Adv. Funct. Mater., 30, 1909054



Fundamental understanding of anisotropic growth in oxide nanocrystals is crucial to establish new synthesis strategies and to tailor the nanoscale electronic, magnetic, optical, and electrocatalytic properties of these particles. While several growth investigations of metal alloy nanoparticles have been reported, mechanistic studies on the growth of ternary oxide materials are still missing. This work constitutes the first study on the evolution of anisotropic growth of manganese–cobalt oxide nanoparticles by monitoring the elemental distribution and morphology during the particle evolution via scanning transmission electron microscopy–X‐ray spectroscopy. A new growth mechanism based on a “solution‐solid‐solid” pathway for mixed manganese cobalt oxides is revealed. In this mechanism, the MnO seed formation occurs in the first step, followed by the surface Co enrichment, which catalyzes the growth along the <100> directions in all the subsequent growth stages, creating rod, cross‐, and T‐shaped mixed metal oxides, which preferentially expose {100} facets. It is shown that the interrelation of both Mn and Co ions initializes the anisotropic growth and presents the range of validity of the proposed mechanism as well as the shape‐determining effect based on the metal‐to‐metal ratio.
Wenming Tong, Mark Forster, Fabio Dionigi, Sören Dresp, Roghayeh Sadeghi Erami, Peter Strasser, Alexander J. Cowan and Pau Farràs

Electrolysis of low-grade and saline surface water

Nature Energy, 5, 367-377



Powered by renewable energy sources such as solar, marine, geothermal and wind, generation of storable hydrogen fuel through water electrolysis provides a promising path towards energy sustainability. However, state-of-the-art electrolysis requires support from associated processes such as desalination of water sources, further purification of desalinated water, and transportation of water, which often contribute financial and energy costs. One strategy to avoid these operations is to develop electrolysers that are capable of operating with impure water feeds directly. Here we review recent developments in electrode materials/catalysts for water electrolysis using low-grade and saline water, a significantly more abundant resource worldwide compared to potable water. We address the associated challenges in design of electrolysers, and discuss future potential approaches that may yield highly active and selective materials for water electrolysis in the presence of common impurities such as metal ions, chloride and bio-organisms.
Sebastian Ott, Alin Orfanidi, Henrike Schmies, Björn Anke, Hong Nhan Nong, Jessica Hübner, Ulrich Gernert, Manuel Gliech, Martin Lerch and Peter Strasser

Ionomer distribution control in porous carbonsupported catalyst layers for high-power and low Pt-loaded proton exchange membrane fuel cells

Nature Materials, 19, 77–85



The reduction of Pt content in the cathode for proton exchange membrane fuel cells is highly desirable to lower their costs. However, lowering the Pt loading of the cathodic electrode leads to high voltage losses. These voltage losses are known to originate from the mass transport resistance of O2 through the platinum–ionomer interface, the location of the Pt particle with respect to the carbon support and the supports’ structures. In this study, we present a new Pt catalyst/support design that substantially reduces local oxygen-related mass transport resistance. The use of chemically modified carbon supports with tailored porosity enabled controlled deposition of Pt nanoparticles on the outer and inner surface of the support particles. This resulted in an unprecedented uniform coverage of the ionomer over the high surface-area carbon supports, especially under dry operating conditions. Consequently, the present catalyst design exhibits previously unachieved fuel cell power densities in addition to high stability under voltage cycling. Thanks to the Coulombic interaction between the ionomer and N groups on the carbon support, homogeneous ionomer distribution and reproducibility during ink manufacturing process is ensured.
Hong Nhan Nong, Hoang Phi Tran, Camillo Spöri, Malte Klingenhof, Lorenz Frevel, Travis Jones, Thorsten Cottre, Bernhard Kaiser, Wolfram Jaegermann, Robert Schlögl, Detre Teschner and Peter Strasser

The Role of Surface Hydroxylation, Lattice Vacancies and Bond Covalency in the Electrochemical Oxidation of Water (OER) on Ni-Depleted Iridium Oxide Catalysts

Zeitschrift für Physikalische Chemie, 234, 787-812



The usage of iridium as an oxygen-evolution-reaction (OER) electrocatalyst requires very high atomefficiencies paired with high activity and stability. Our efforts during the past 6 years in the Priority Program 1613 funded by the Deutsche Forschungsgemeinschaft (DFG) were focused to mitigate the molecular origin of kinetic overpotentials of Ir-based OER catalysts and to design new materials to achieve that Ir-based catalysts are more atom and energy efficient, as well as stable. Approaches involved are: use of bimetallic mixed metal oxide materials where Ir is combined with cheaper transition metals as starting materials, use of dealloying concepts of nanometer sized core-shell particle with a thin noble metal oxide shell combined with a hollow or cheap transition metal-rich alloy core, and use of corrosion-resistant high-surface-area oxide support materials. In this mini review, we have highlighted selected advances in our understanding of Ir–Ni bimetallic oxide electrocatalysts for the OER in acidic environments.

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