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An active and stable hydrogen evolution electrocatalyst composed of MoO2 surface nanorod arrays was prepared using high-temperature reductive annealing. Electrodes with an area of 78.5 cm2 were evaluated in a three-cell AEM electrolyser stack.

Aqueous sodium-ion batteries based on PrussianBlue Analogues (PBA) are considered as promising and scalablecandidates for stationary energy storage systems, where longevityand cycling stability are assigned utmost importance to maintaineconomic viability. Although degradation due to active materialdissolution is a common issue of battery electrodes, it is hardlyobservable directly due to a lack of in operando techniques, makingit challenging to optimize the performance of electrodes. Byoperating Na2Ni[Fe(CN)6] and Na2Co[Fe(CN)6] model electrodesin a flow-cell setup connected to an inductively coupled plasmamass spectrometer, in this work, the dynamics of constituenttransition-metal dissolution during the charge−discharge cycleswas monitored in real time. At neutral pHs, the extraction of nickeland cobalt was found to drive the degradation process during charge−discharge cycles. It was also found that the nature of anionspresent in the electrolytes has a significant impact on the degradation rate, determining the order ClO4− > NO3− > Cl− > SO42− withdecreasing stability from the perchlorate to sulfate electrolytes. It is proposed that the dissolution process is initiated by detrimentalspecific adsorption of anions during the electrode oxidation, therefore scaling with their respective chemisorption affinity. This studyinvolves an entire comparison of the effectiveness of common stabilization strategies for PBAs under very fast (dis)chargingconditions at 300C, emphasizing the superiority of highly concentrated NaClO4 with almost no capacity loss after 10 000 cycles forNa2Ni[Fe(CN)6].KEYWORDS: Na-ion aqueous batteries, Prussian Blue Analogues, sodium nickel hexacyanoferrate, ICP-MS, active material dissolution,degradation

Molecular catalysts are promising oxygen evolution promoters in conjunction with photoanodes for solar water splitting. Maintaining the stability of both photoabsorber and cocatalyst is still a prime challenge, with many efforts tackling this issue through sophisticated material designs. Such approaches often mask the importance of the electrode‐electrolyte interface and overlook easily tunable system parameters, such as the electrolyte environment, to improve efficiency. We provide a systematic study on the activity‐stability relationship of a prominent Fe2O3 photoanode modified with Ir molecular catalysts using in situ mass spectroscopy. After gaining detailed insights into the dissolution behavior of the Ir cocatalyst, a comprehensive pH study is conducted to probe the impact of the electrolyte on the performance. An inverse trend in Fe and Ir stability is found, with the best activity‐stability synergy obtained at pH 9.7. The results bring awareness to the overall photostability and electrolyte engineering when advancing catalysts for solar water splitting.

A major goal within the CO2 electrolysis community is to replace the generally used Ir anode catalyst with a more abundant material, which is stable and active for water oxidation under process conditions. Ni is widely applied in alkaline water electrolysis, and it has been considered as a potential anode catalyst in CO2 electrolysis. Here we compare the operation of electrolyzer cells with Ir and Ni anodes and demonstrate that, while Ir is stable under process conditions, the degradation of Ni leads to a rapid cell failure. This is caused by two parallel mechanisms: (i) a pH decrease of the anolyte to a near neutral value and (ii) the local chemical environment developing at the anode (i.e., high carbonate concentration). The latter is detrimental for zero-gap electrolyzer cells only, but the first mechanism is universal, occurring in any kind of CO2 electrolyzer after prolonged operation with recirculated anolyte.

Stabilization of cathode catalysts in hydrogen-fueled proton-exchange membrane fuel cells (PEMFCs) is paramount to their widespread commercialization. Targeting that aim, Pt-Au alloy catalysts with various compositions (Pt

By photodeposition of CrOx on SrTiO3-based semiconductors doped with aliovalent Mg(II) and functionalized with Ni/NiOx catalytic nanoparticles (economically significantly more viable than commonly used Rh catalysts), an increase in apparent quantum yield (AQYs) from ∼10 to 26% in overall water splitting was obtained. More importantly, deposition of CrOx also significantly enhances the stability of Ni/NiO nanoparticles in the production of hydrogen, allowing sustained operation, even in intermittent cycles of illumination. In situ elemental analysis of the water constituents during or after photocatalysis by inductively coupled plasma mass spectrometry/optical emission spectrometry shows that after CrOx deposition, dissolution of Ni ions from Ni/NiOx-Mg:SrTiO3 is significantly suppressed, in agreement with the stabilizing effect observed, when both Mg dopant and CrOx are present. State-of-the-art electron microscopy and energy-dispersive X-ray spectroscopy (EDX) and electron energy-loss spectroscopy (EELS) analyses demonstrate that upon preparation, CrOx is photodeposited in the vicinity of several, but not all, Ni/NiOx particles. This implies the formation of a Ni-Cr mixed metal oxide, which is highly effective in water reduction. Inhomogeneities in the interfacial contact, evident from differences in contact angles between Ni/NiOx particles and the Mg:SrTiO3 semiconductor, likely affect the probability of reduction of Cr(VI) species during synthesis by photodeposition, explaining the observed inhomogeneity in the spatial CrOx distribution. Furthermore, by comparison with undoped SrTiO3, Mg-doping appears essential to provide such favorable interfacial contact and to establish the beneficial effect of CrOx. This study suggests that the performance of semiconductors can be significantly improved if inhomogeneities in interfacial contact between semiconductors and highly effective catalytic nanoparticles can be resolved by (surface) doping and improved synthesis protocols.

The production of hydrogen via a proton-exchange membrane water electrolyzer (PEM-WE) is directly dependent on the rational design of electrocatalysts for the anodic oxygen evolution reaction (OER), which is the bottleneck of the process. Here, we present a smart design strategy for enhancing Ir utilization and stabilization. We showcase it on a catalyst, where Ir nanoparticles are efficiently anchored on a conductive support titanium oxynitride (TiON x ) dispersed over carbon-based Ketjen Black and covered by a thin layer of copper (Ir/CuTiON x /C), which gets removed in the preconditioning step. Electrochemical OER activity, stability, and structural changes were compared to the Ir-based catalyst, where Ir nanoparticles without Cu are deposited on the same support (Ir/TiON x /C). To study the effect of the sacrificial less-noble metal layer on the catalytic performance of the synthesized material, characterization methods, namely X-ray powder diffraction, X-ray photoemission spectroscopy, and identical location transmission electron microscopy were employed and complemented with scanning flow cell coupled to an inductively coupled plasma mass spectrometer, which allowed studying the online dissolution during the catalytic reaction. Utilization of these advanced methods revealed that the sacrificial Cu layer positively affects both Ir OER mass activity and its durability, which was assessed via S-number, a recently reported stability metric. Improved activity of Cu analogue was ascribed to the higher surface area of smaller Ir nanoparticles, which are better stabilized through a strong metal-support interaction (SMSI) effect.

Platinum-based bimetallic alloys have been largely investigated during the last few years as a valid alternative to bare Pt cathode catalysts for proton-exchange membrane fuel cells (PEMFCs) to improve their cost-efficiency. Nonetheless, Pt bimetallic alloys are characterized by a reduced stability, which is poorly understood at a fundamental level. It is thus essential to describe the entire chain of interconnected degradation mechanisms to formulate a comprehensive model of catalyst degradation that will help interpret bimetallic alloy behavior in real complex fuel cell systems. By combining in situ inductively coupled plasma mass spectroscopy, in situ grazing-incidence small-angle X-ray scattering, and ex situ scanning electron microscopy, we have studied the morphological evolution of PtXNi100–X model catalysts with different Ni contents (ranging from 0 to 75%) undergoing potentiodynamic cycling to two different upper potentials mimicking the different operational conditions of a PEMFC: 1.0 and 1.3 VRHE. Data analysis allowed us to develop a methodology to distinguish the influence of Ni dissolution, particle coalescence, and Ostwald ripening on particle size distribution and interparticle distance and to realize time-dependent interplay maps to highlight the timeframe in which the aforementioned phenomena are prevailing or coexisting. Results show that Ni dissolution is the only phenomenon inducing morphological evolution when the lower upper potential is chosen. On the contrary, at 1.3 VRHE, Ni dissolution is rapidly overcome by particle coalescence at first and by Ostwald ripening in the later stages of the investigated time range. The onset of every phenomenon was found to occur earlier in time for larger values of Ni concentrations.

The structure of IrO$_{2}$ during the oxygen evolution reaction (OER) was studied by operando X-ray absorption spectroscopy (XAS) at the Ir L$_{3}$-edge to gain insight into the processes that occur during the electrocatalytic reaction at the anode during water electrolysis. For this purpose, calcined and uncalcined IrO$_{2}$ nanoparticles were tested in an operando spectroelectrochemical cell. In situ XAS under different applied potentials uncovered strong structural changes when changing the potential. Modulation excitation spectroscopy combined with XAS enhanced the information on the dynamic changes significantly. Principal component analysis (PCA) of the resulting spectra as well as FEFF9 calculations uncovered that both the Ir L$_{3}$-edge energy and the white line intensity changed due to the formation of oxygen vacancies and lower oxidation state of iridium at higher potentials, respectively. The deconvoluted spectra and their components lead to two different OER modes. It was observed that at higher OER potentials, the well-known OER mechanisms need to be modified, which is also associated with the stabilization of the catalyst, as confirmed by in situ inductively coupled plasma mass spectrometry (ICP-MS). At these elevated OER potentials above 1.5 V, stronger Ir���Ir interactions were observed. They were more dominant in the calcined IrO$_{2}$ samples than in the uncalcined ones. The stronger Ir���Ir interaction upon vacancy formation is also supported by theoretical studies. We propose that this may be a crucial factor in the increased dissolution stability of the IrO$_{2}$ catalyst after calcination. The results presented here provide additional insights into the OER in acid media and demonstrate a powerful technique for quantifying the differences in mechanisms on different OER electrocatalysts. Furthermore, insights into the OER at a fundamental level are provided, which will contribute to further understanding of the reaction mechanisms in water electrolysis.

The stability of perovskite oxide catalysts for the oxygen evolution reaction (OER) plays a critical role in their applicability in water splitting concepts. Decomposition of perovskite oxides under applied potential is typically linked to cation leaching and amorphization of the material. However, structural changes and phase transformations at the catalyst surface were also shown to govern the activity of several perovskite electrocatalysts under applied potential. Hence, it is crucial for the rational design of durable perovskite catalysts to understand the interplay between the formation of active surface phases and stability limitations under OER conditions. In the present study, we reveal a surface-dominated activation and deactivation mechanism of the prominent electrocatalyst La

Despite intensive investigations for unravelling the water splitting reaction, the catalyst behavior during the oxygen evolution reaction (OER) is still not fully understood. This is especially true under more demanding conditions like high potentials and high temperatures. Rotating disk electrode measurements show a gradual increase of OER current when increasing the temperature up to 80 °C. However, strong bubble formation at elevated temperatures makes in‐situ characterization of the catalyst challenging. Here we utilize an in‐situ electrochemical and heated flow cell, which aims at an efficient removal of bubbles from the catalyst surface and enables structural studies by X‐ray absorption spectroscopy (XAS) at temperatures up to 80 °C. Changes in the Ir L3‐edge X‐ray absorption near edge spectra (XANES) were observed with respect to the white line position and principal components related to structural changes were extracted. At temperatures of 60 °C and above, the white line position of XANES spectra reaches a steady state, which is possibly caused by an equilibrium of different Ir oxidation states. These findings provide first spectroscopic insights in the behavior of OER catalysts at elevated temperatures which are typical for industrial applications and rarely addressed until now.

The lack of efficient and durable proton exchange membrane fuel cell electrocatalysts for the oxygen reduction reaction is still restraining the present hydrogen technology. Graphene-based carbon materials have emerged as a potential solution to replace the existing carbon black (CB) supports however, their potential was never fully exploited as a commercial solution because of their more demanding properties. Here, a unique and industrially scalable synthesis of platinum-based electrocatalysts on graphene derivative (GD) supports is presented. With an innovative approach, highly homogeneous as well as high metal loaded platinum-alloy (up to 60 wt %) intermetallic catalysts on GDs are achieved. Accelerated degradation tests show enhanced durability when compared to the CB-supported analogues including the commercial benchmark. Additionally, in combination with X-ray photoelectron spectroscopy Auger characterization and Raman spectroscopy, a clear connection between the sp$^2$ content and structural defects in carbon materials with the catalyst durability is observed. Advanced gas diffusion electrode results show that the GD-supported catalysts exhibit excellent mass activities and possess the properties necessary to reach high currents if utilized correctly. We show record-high peak power densities in comparison to the prior best literature on platinum-based GD-supported materials which is promising information for future application.

The stability of perovskite oxide catalysts for the oxygen evolution reaction (OER) plays a critical role for their applicability in water splitting concepts. Decomposition of perovskite oxides under applied potential is typically linked to cation leaching and amorphization of the material. However, structural changes and phase transformations at the catalyst surface were also shown to govern the activity of several perovskite electro-catalysts under applied potential. Hence, it is crucial for the rational design of durable perovskite catalysts to understand the interplay between the formation of active surface phases and stability limitations under OER conditions. In the present study, we reveal a surface-dominated activation and deactivation mechanism of the prominent electrocatalyst La0.6Sr0.4CoO3-ẟ under steady-state OER conditions. Using a multi-scale micros-copy and spectroscopy approach, we identify evolving Co-oxyhydroxide as catalytically active surface species and La-hydroxide as inactive species involved in the transient degradation behavior of the catalyst. While the leaching of Sr results in the formation of mixed surface phases, that can be considered as a part of the active surface, the gradual depletion of Co from a self-assembled active CoO(OH) phase and the relative enrichment of passivating La(OH)3 at the electrode surface results in the failure of the perovskite catalyst under applied potential.

Extensive research efforts are currently dedicated to the search for new electrocatalyst materials in which expensive and rare noble metals are replaced with cheaper and more abundant transition metals. Recently, numerous alloys, oxides, and composites with such metals have been identified as highly active electrocatalysts through the use of high‐throughput screening methods with the help of activity descriptors. Up to this point, stability has lacked such descriptors. Hence, we elucidate the role of intrinsic metal/oxide properties on the corrosion behavior of representative 3d, 4d, and 5d transition metals. Electrochemical dissolution of nine transition metals is quantified using online inductively coupled plasma mass spectrometry (ICP‐MS). Based on the obtained dissolution data in alkaline and acidic media, we establish clear periodic correlations between the amount of dissolved metal, the cohesive energy of the metal atoms (E coh), and the energy of oxygen adsorption on the metal (ΔH O,ads). Such correlations can support the knowledge‐driven search for more stable electrocatalysts., In this study, intrinsic metal descriptors based on theoretical considerations are linked to experimentally determined dissolution rates. Clear trends are identified between the dissolution during oxide formation and the metal–metal cohesive energy, as well as between the dissolution during the reduction of an oxide and the metal–oxygen adsorption energy.

Pt dissolution has already been intensively studied in aqueous model systems and many mechanistic insights have been gained. Nevertheless, transfer of new knowledge to real‐world fuel cell systems is still a significant challenge. To close this gap, we present a novel in situ method combining a gas diffusion electrode (GDE) half‐cell with inductively coupled plasma mass spectrometry (ICP‐MS). With this setup, Pt dissolution in realistic catalyst layers and the transport of dissolved Pt species through Nafion membranes were evaluated directly. We observed that 1) specific Pt dissolution increased significantly with decreasing Pt loading, 2) in comparison to experiments on aqueous model systems with flow cells, the measured dissolution in GDE experiments was considerably lower, and 3) by adding a membrane onto the catalyst layer, Pt dissolution was reduced even further. All these phenomena are attributed to the varying mass transport conditions of dissolved Pt species, influencing re‐deposition and equilibrium potential., An in situ technique is presented that closes the gap between catalyst degradation studies in real devices and fundamental electrochemical analyses. The method involves direct measurement of platinum dissolution in realistic catalyst layers and through Nafion membranes. The impact of catalyst loading and electrode–electrolyte interface on platinum dissolution, as well as transport behavior of dissolved Pt species through Nafion membranes, are investigated.

The electrochemical activity of modern Fe-N-C electrocatalysts in alkaline media is on par with that of platinum. For successful application in fuel cells (FCs), however, also high durability and longevity must be demonstrated. Currently, a limited understanding of degradation pathways, especially under operando conditions, hinders the design and synthesis of simultaneously active and stable Fe-N-C electrocatalysts. In this work, using a gas diffusion electrode half-cell coupled with inductively coupled plasma mass spectrometry setup, Fe dissolution is studied under conditions close to those in FCs, that is, with a porous catalyst layer (CL) and at current densities up to -125 mA·cm

Understanding metal surface reconstruction during operation is of the uttermost importance in heterogeneous catalysis as it directly affects the available active sites. However, surface reconstruction is notoriously difficult to study because of the dynamic nature of the phenomena behind it. Here, we report on the mechanism and the intermediates, which drive the rearrangement of copper catalysts during the electrochemical CO2 reduction reaction. In-situ methods, including mass spectrometry and fluorescence spectroscopy, evidence a dissolution – redeposition process mediated by transient species containing copper in +1 oxidation state. Theory identifies copper-adsorbate complexes which form in solution under operating conditions. Copper carbonyls and oxalates emerge as the major reaction-specific species driving copper reconstruction. This work motivates future studies to specifically target these compounds to improve the catalyst operational stability in the electrochemical CO2 reduction reaction.

The selective electrooxidation of 2-propanol to acetone can be used in fuel cells which, when combined with the transfer hydrogenation of acetone from liquid organic hydrogen carriers, will enable the realization of hydrogen economy without using molecular hydrogen gas for storage and transportation. We study the reaction on platinum and platinum-ruthenium nanocatalysts using unique tools for the real-time characterization of reaction and dissolution products. Acetone is the primary product on all investigated catalysts, and only traces of CO2 form at high potentials. We propose that the reaction occurs on Pt-Ru ensemble sites at low potentials and on Pt-Pt sites at high potentials. Dissolution of surface ruthenium atoms leads to suppression of the process at low overpotential. The main shortcomings to be addressed for an efficient catalyst performance are (a) the narrow potential range in which the bimetallic catalyst is active, (b) the surface poisoning from adsorbed acetone, and (c) the dissolution of ruthenium.

Application of oxide supports is considered as a viable approach to decrease iridium loading in oxygen evolution reaction catalysis in acid electrolyte. While the most of the promising oxides are poor conductors, the need for doping is typically taken as granted, and a representative example is tin dioxide. There are still, however, serious concerns on the feasibility of this approach as we lack consensus on any activity gain by using such oxides, while doubts on stability are numerous. In this work, a set of catalyst/support combinations including two catalysts, viz. hydrous (IrOx ) and rutile (IrO2) iridium oxides, and four supports, viz. SnO2 and Sb‐ (ATO), F‐ (FTO), and In‐doped (ITO) SnO2, are synthesized and characterized by a selection of complementary experimental techniques including rotating disk electrode and on‐line inductively coupled plasma mass spectrometry. It is found that the electrochemical activity in acid media of supported Ir catalysts is essentially the same, independent on presence or absence of dopants. Sb and In dopants are shown to be unstable and cause an increased dissolution of Sn. Besides, the degradation of the doped supports results in destabilization of iridium oxides. These results raise doubts on the real need for the use of dopants in SnO2‐based catalyst supports for electrochemical water splitting.

Polymer electrolyte membrane fuel cells (PEMFCs) are highly attractive for use in electric vehicles. In PEMFCs, small particle sizes of the Pt catalyst are required to increase Pt utilization, whic...

Comprehensive understanding of the catalyst corrosion dynamics is a prerequisite for the development of an efficient cathode catalyst in proton-exchange membrane fuel cells. To reach this aim, the behavior of fuel cell catalysts must be investigated directly under reaction conditions. Herein, we applied a strategic combination of in situ/online techniques: in situ electrochemical atomic force microscopy, in situ grazing incidence small angle X-ray scattering, and electrochemical scanning flow cell with online detection by inductively coupled plasma mass spectrometry. This combination of techniques allows in-depth investigation of the potential-dependent surface restructuring of a PtNi model thin film catalyst during potentiodynamic cycling in an aqueous acidic electrolyte. The study reveals a clear correlation between the upper potential limit and structural behavior of the PtNi catalyst, namely, its dealloying and coarsening. The results show that at 0.6 and 1.0 VRHE upper potentials, the PtNi catalyst essentially preserves its structure during the entire cycling procedure. The crucial changes in the morphology of PtNi layers are found to occur at 1.3 and 1.5 VRHE cycling potentials. Strong dealloying at the early stage of cycling is substituted with strong coarsening of catalyst particles at the later stage. The coarsening at the later stage of cycling is assigned to the electrochemical Ostwald ripening process.

High-impact photoelectrode materials for photoelectrochemical (PEC) water splitting are distinguished by synergistically attaining high photoactivity and stability at the same time. With numerous efforts toward optimizing the activity, the bigger challenge of tailoring the durability of photoelectrodes to meet industrially relevant levels remains. In situ photostability measurements using flow cells hold great promise in understanding stability-related properties1-3 compared to traditional procedures, such as measuring the drop in photocurrent over time at 1.23 VRHE. In this work, a photoelectrochemical scanning flow cell connected to an inductively coupled plasma mass spectrometer (PEC-ICP-MS) and equipped with a solar simulator, Air Mass 1.5 G filter, and monochromator was developed (Figure 1A). The established system is capable of independently assessing basic PEC metrics, such as photopotential, photocurrent, incident photon to current efficiency (IPCE), and band gap in a high-throughput manner, as well as the in situ photocorrosion behavior of photoelectrodes under standardized and realistic light conditions by coupling it to an ICP-MS.4 In situ photocorrosion measurements conducted on spray-coated WO3 revealed that dissolution starts at 0.8 VRHE with the dissolution rate rapidly increasing past 1.2 VRHE, coinciding with the onset of the saturation photocurrent (Figure 1B). Wavelength-dependent photodegradation measurements show that WO3 only dissolved when irradiated with wavelengths lower than its band gap (Figure 1C). By using standardized illumination conditions such as AM 1.5 G under 1 Sun, the obtained dissolution characteristics are translatable to actual devices under realistic light conditions. The gained insights can then be utilized to advance synthesis and design approaches of novel PEC materials with improved photostability. Another aspect of flow cell systems is that they are well suited for operation in a high-throughput manner. In fact, scanning droplet cells have been successfully employed for rapid (photo)electrochemical screening of (photo)electrocatalyst libraries.5, 6 In here, we demonstrate proof-of-concept approaches for a full automation of the presented system to establish a platform that is capable of not only performing complete sets of PEC measurements but at the same time assess the in situ photostability of a photoelectrode material library. Such a platform would enable material discovery, which is tailored to search not only for the most active but also for the most stable PEC material. References Knöppel, J.; Zhang, S.; Speck, F. D.; Mayrhofer, K. J. J.; Scheu, C.; Cherevko, S., Time-resolved analysis of dissolution phenomena in photoelectrochemistry – A case study of WO3 photocorrosion. Electrochem. Commun. 2018, 96, 53-56. Dworschak, D.; Brunnhofer, C.; Valtiner, M., Photocorrosion of ZnO Single Crystals during Electrochemical Water Splitting. ACS Appl Mater Interfaces 2020, 12 (46), 51530-51536. Zhang, S.; Rohloff, M.; Kasian, O.; Mingers, A. M.; Mayrhofer, K. J. J.; Fischer, A.; Scheu, C.; Cherevko, S., Dissolution of BiVO4 Photoanodes Revealed by Time-Resolved Measurements under Photoelectrochemical Conditions. The Journal of Physical Chemistry C 2019, 123 (38), 23410-23418. Jenewein, K. J.; Kormányos, A.; Knöppel, J.; Mayrhofer, K. J. J.; Cherevko, S., Accessing In Situ Photocorrosion under Realistic Light Conditions: Photoelectrochemical Scanning Flow Cell Coupled to Online ICP-MS. ACS Measurement Science Au 2021, 1 (2), 74-81. Gregoire, J. M.; Xiang, C.; Liu, X.; Marcin, M.; Jin, J., Scanning droplet cell for high throughput electrochemical and photoelectrochemical measurements. Rev. Sci. Instrum. 2013, 84 (2), 024102. Sliozberg, K.; Schafer, D.; Erichsen, T.; Meyer, R.; Khare, C.; Ludwig, A.; Schuhmann, W., High-throughput screening of thin-film semiconductor material libraries I: system development and case study for Ti-W-O. ChemSusChem 2015, 8 (7), 1270-8. Figure 1