This Review addresses the technical challenges, scientific basis, recent progress, and outlook with respect to the stability and degradation of catalysts for the oxygen evolution reaction (OER) operating at electrolyzer anodes in acidic environments with an emphasis on ion exchange membrane applications. First, the term "catalyst stability" is clarified, as well as current performance targets, major catalyst degradation mechanisms, and their mitigation strategies. Suitable in situ experimental methods are then evaluated to give insight into catalyst degradation and possible pathways to tune OER catalyst stability. Finally, the importance of identifying universal figures of merit for stability is highlighted, leading to a comprehensive accelerated lifetime test that could yield comparable performance data across different laboratories and catalyst types. The aim of this Review is to help disseminate and stress the important relationships between structure, composition, and stability of OER catalysts under different operating conditions.

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Electrochemical hydrogen peroxide (H 2 O 2 ) production by two-electron oxygen reduction is a promising alternative process to the established industrial anthraquinone process. Current challenges relate to finding cost-effective electrocatalysts with high electrocatalytic activity, stability, and product selectivity. Here, we explore the electrocatalytic activity and selectivity toward H 2 O 2 production of a number of distinct nitrogen-doped mesoporous carbon catalysts and report a previously unachieved H 2 O 2 selectivity of ∼95−98% in acidic solution. To explain our observations, we correlate their structural, compositional, and other physicochemical properties with their electrocatalytic performance and uncover a close correlation between the H 2 O 2 product yield and the surface area and interfacial zeta potential. Nitrogen doping was found to sharply boost H 2 O 2 activity and selectivity. Chronoamperometric H 2 O 2 electrolysis confirms the exceptionally high H 2 O 2 production rate and large H 2 O 2 faradaic selectivity for the optimal nitrogen-doped CMK-3 sample in acidic, neutral, and alkaline solutions. In alkaline solution, the catalytic H 2 O 2 yield increases further, where the production rate of the HO 2 − anion reaches a value as high as 561.7 mmol g catalyst −1 h −1 with H 2 O 2 faradaic selectivity above 70%. Our work provides a guide for the design, synthesis, and mechanistic investigation of advanced carbon-based electrocatalysts for H 2 O 2 production.

Seawater electrolysis faces fundamental chemical challenges, such as the suppression of highly detrimental halogen chemistries, which has to be ensured by selective catalyst and suitable operating conditions. In the present study, nanostructured NiFe‐layered double hydroxide and Pt nanoparticles are selected as catalysts for the anode and cathode, respectively. The seawater electrolyzer is tested successfully for 100 h at maximum current densities of 200 mA cm−2 at 1.6 V employing surrogate sea water and compared to fresh water feeds. Different membrane studies are carried out to reveal the cause of the current density drop. During long‐term dynamic tests, under simulated day‐night cycles, an unusual cell power performance recovery effect is uncovered, which is subsequently harnessed in a long‐term diurnal day‐night cycle test. The natural day‐night cycles of the electrolyzer input power can be conceived as a reversible catalyst materials recovery treatment of the device when using photovoltaic electricity sources. To understand the origin of this reversible recovery on a molecular materials level, in situ extended X‐ray absorption fine structure and X‐ray near‐edge region spectra are applied.

We report and study the translation of exceptionally high catalytic oxygen electroreduction activities of molybdenum-doped octahedrally shaped PtNi­(Mo) nanoparticles from conventional thin-film rotating disk electrode screenings (3.43 ± 0.35 A mgPt –1 at 0.9 VRHE) to membrane electrode assembly (MEA)-based single fuel cell tests with sustained Pt mass activities of 0.45 A mgPt –1 at 0.9 Vcell, one of the highest ever reported performances for advanced shaped Pt alloys in real devices. Scanning transmission electron microscopy with energy dispersive X-ray analysis (STEM-EDX) reveals that Mo preferentially occupies the Pt-rich edges and vertices of the element-anisotropic octahedral PtNi particles. Furthermore, by combining in situ wide-angle X-ray spectroscopy, X-ray fluorescence, and STEM-EDX elemental mapping with electrochemical measurements, we finally succeeded to realize high Ni retention in activated PtNiMo nanoparticles even after prolonged potential-cycling stability tests. Stability losses at the anodic potential limits were mainly attributed to the loss of the octahedral particle shape. Extending the anodic potential limits of the tests to the Pt oxidation region induced detectable Ni losses and structural changes. Our study shows on an atomic level how Mo adatoms on the surface impact the Ni surface composition, which, in turn, gives rise to the exceptionally high experimental catalytic ORR reactivity and calls for strategies on how to preserve this particular surface composition to arrive at performance stabilities comparable with state-of-the-art spherical dealloyed Pt core–shell catalysts.

Recent progress in the activity improvement of anode catalysts for acidic electrochemical water splitting is largely achieved through empirical studies of iridium-based bimetallic oxides. Practical, experimentally accessible, yet general predictors of catalytic OER activity have remained scarce. This study investigates iridium and iridium–nickel thin film model electrocatalysts for the OER and identifies a set of general ex situ properties that allow the reliable prediction of their OER activity. Well-defined Ir-based catalysts of various chemical nature and composition were synthesized by magnetron sputtering. Correlation of physicochemical and electrocatalytic properties revealed two experimental OER activity descriptors that are able to predict trends in the OER activity of unknown Ir-based catalyst systems. More specifically, our study demonstrates that the IrIII+- and OH-surface concentration of the oxide catalyst constitute closely correlated and generally applicable OER activity predictors. On the basis of these predictors, an experimental volcano relationship of Ir-based OER electrocatalysts is presented and discussed.

We report a comparative study on the influence of generic electrochemical activation–oxidation protocols on the resulting surface oxides of Ir(1 1 1) and (1 1 0) and Ru(0 0 0 1) single crystals and their electrocatalytic reactivity for the oxygen evolution reaction. Well‐defined single‐crystal electrodes were prepared in a custom‐made chamber that combines inductive thermal annealing and electrochemistry. The clean surfaces were analyzed for their electrocatalytic oxygen evolution activities and oxidation behavior. Three different oxidation protocols were used, which revealed a strong activity dependence on the duration and upper potential limit of the electrochemical oxidation. The resulting changes of the surface were followed by using cyclic voltammetry and impedance spectroscopy. Important differences between the two faces of Ir in terms of surface morphology of the formed oxide were identified, which allowed us to draw conclusions for preferable crystal faces in nanoparticle catalysts.

Hydrogen production by proton exchange membrane (PEM) water electrolysis is among the promising energy storage solutions to buffer an increasingly volatile power grid employing significant amounts of renewable energies. In PEM electrolysis research, 24 h galvanostatic measurements are the most common initial stability screenings and up to 5,000 h are used to assess extended stability, while commercial stack runtimes are within the 20,000–50,000 h range. In order to obtain stability data representative of commercial lifetimes with significantly reduced test duration an accelerated degradation test (ADT) was suggested by our group earlier. Here, we present a study on the broad applicability of the suggested ADT in RDE and CCM measurements and showcase the advantage of transient over static operation for enhanced catalyst degradation studies. The suggested ADT-1.6 V protocol allows unprecedented, reproducible and quick assessment of anode catalyst long-term stability, which will strongly enhance degradation research and reliability. Furthermore, this protocol allows to bridge the gap between more fundamental RDE and commercially relevant CCM studies.