There is an ongoing debate on elucidating the actual role of Fe impurities in alkaline water electrolysis, acting either as reactivity mediators or as co-catalysts through synergistic interaction ...with the main catalyst material. This perspective summarizes the most prominent oxygen evolution reaction (OER) mechanisms mostly for Ni-based oxides as model transition metal catalysts and highlights the effect of Fe incorporation on the catalyst surface in the form of impurities originating from the electrolyte or co-precipitated in the catalyst lattice, in modulating the OER reaction kinetics, mechanism and stability.
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In this report, the coupling and dispersion characteristics of discrete and coalesced square resonators was investigated in the MHz regime. Resonators with one and three gaps were considered. When ...the resonators are not in direct contact, the number of gaps has little effect upon the total coupling, which is negative. When the resonators are connected so that they share one side, the coupling can change drastically depending on the number of gaps. In particular, when the shared side has a gap, the total coupling coefficient switches to positive values, making it possible for forward travelling waves to propagate on arrays. Experimental, numerical and analytical data verify this behaviour.
Plotting the roadmap of future “renewable energy highway” requires drastic technological advancement of devices like electrolyzers and fuel cells. Technological breakthrough is practically impossible ...without advanced fundamental understanding of interfacial energy conversion processes, including electrocatalytic water splitting. Particularly challenging is the oxygen evolution reaction which imposes high demands on the long-term activity of electrocatalysts and electrode support materials. To cross the “Rubicon” and in a deterministic manner claim that we developed principles of rational catalyst design, we need first to comprehend the determinants of electrocatalytic activity as well as character of their time evolution. How reliable are reported activity and stability trends, could we interrelate activity and stability, and how meaningful that relation really is are some of the important questions that have to be tackled in building of a more comprehensive view on critically important anodic oxygen evolution.
A carbon supported platinum electrode in a bismuth saturated solution at a carefully chosen potential is capable of oxidizing glycerol to dihydroxyacetone with 100% selectivity. In the absence of ...bismuth, the primary alcohol oxidation is dominant. Using a combination of online HPLC and in situ FTIR, it is shown that Bi blocks the pathway for primary oxidation but also provides a specific Pt–Bi surface site poised for secondary alcohol oxidation.
A colloidal synthesis approach is used to prepare supported proton exchange membrane fuel cell (PEMFC) catalysts with various Pt loadings – from low to extremely high ones. The catalyst samples are ...used to continue our investigation of the role of the Pt:C ratio in the degradation processes. The influence of the platinum loading on the electrochemical surface area (ECSA) loss is evaluated in a systematic electrochemical study by using two commercially available carbon blacks, namely Vulcan XC72R and Ketjenblack EC-300J. Accelerated degradation tests simulating load cycle and start-up/shutdown conditions are carried out in accordance with the Fuel Cell Commercialization Conference of Japan (FCCJ) recommendations. Under conditions simulating the load cycle of PEM fuel cells no unambiguous correlation between the ECSA loss and the Pt:C ratio is found. By contrast, under conditions simulating the repetitive start-up/shutdown processes of PEMFCs the ECSA loss first increases with increasing Pt loading. However, it decreases again for very high loadings. Furthermore, the Vulcan samples exhibited higher ECSA losses than the Ketjenblack samples, indicating the important role of the physical and chemical properties of pristine carbon supports in the carbon degradation mechanism.
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•Study of influence of Pt:C ratio on the degradation behaviour of Pt/C catalysts.•Pt:C ratio influences degradation under start-up/shutdown conditions.•Pt:C ratio has small influence on degradation under load cycles.•Degradation on Vulcan XC72R substantial higher than on Ketjenblack EC-300.
The oxygen evolution reaction (OER) is the limiting step in splitting water into its constituents, hydrogen and oxygen. Hence, research on potential OER catalysts has become the focus of many ...studies. In this work, we investigate capable OER catalysts but focus on catalyst stability, which is, especially in this case, at least equally as important as catalyst activity. We propose a specialized setup for monitoring the corrosion profiles of metal oxide catalysts during a stability testing protocol, which is specifically designed to standardize the investigation of OER catalysts by means of differentiating between catalyst corrosion and deactivation, oxygen evolution efficiency, and catalyst activity. For this purpose, we combined an electrochemical flow cell (EFC) with an oxygen sensor and an inductively coupled plasma–optical emission spectrometry (ICP-OES) system for the simultaneous investigation of catalyst deactivation, activity, and faradaic efficiency of catalysts. We tested various catalysts, with IrO2 and NiCoO2 used as benchmark materials in acidic and alkaline environment, respectively. The scalability of our setup will allow the user to investigate catalytic materials with supports of higher surface area than those which are typical for microelectrochemical flow cells (thus, under conditions more similar to those of commercial electrolyzers).
We report a simple and effective electrochemical method to remove Fe impurities from commercial KOH electrolyte. We therefore utilize a MoS2 catalyst deposited on porous Ni foam as both the anode and ...cathode in a two-electrode electrolysis setup. After 12 h of constant galvanostatic electrolysis at 100 mA, the Fe impurities from the KOH electrolyte were successfully removed, as confirmed by means of inductively coupled plasma optical emission spectroscopy analysis. In the purified KOH, a Ni–Co3O4 composite oxide catalyst showed no Fe-induced activation. In contrast, we directly observed the uptake of Fe on the Ni–Co3O4 catalyst from the nontreated electrolyte during catalyst operation using a coupled spectroelectrochemical setup. Interestingly, we further identified an influence on the dissolution behavior of Ni and Co in the presence of Fe impurities. Whereas hitherto mainly the activation effect of Fe impurities has been discussed, we hereby show that they additionally suppress corrosion under reaction conditions. Using our fast and low-cost method for the purification of large amounts of electrolyte, catalyst materials can be widely studied without these additional effects induced by Fe impurities in commercial KOH.
Almost 15 years ago, first papers appeared, in which the density functional theory (DFT) was used to predict activity trends of electrocatalytic reactions. That was a major contribution of ...computational chemistry in building the theory of electrocatalysis. The possibility of computational electrocatalyst design had a massive impact on the way of thinking in modern electrocatalysis. At the same time, substantial criticism towards popular DFT models was developed during the years, due to the oversimplified view on electrified interfaces. Having this in mind, this work proposes an experimental methodology for quantitative description of adsorption energies at solid/liquid interfaces based on the Kelvin probe technique. The introduced approach already gives valuable trends in adsorption energies while in the future should evolve into an additional source of robust values that could complement existing DFT results. The pillars of the new methodology are established and verified experimentally with very promising initial results.
Design of active and stable electrocatalysts for the oxygen evolution reaction (OER) requires in‐depth understanding of the electrocatalyst properties and interfacial structural dynamics during OER. ...One of the essential insights for advanced electrocatalyst design is vivid understanding of the drivers and mechanisms of dissolution of electrocatalysts. In this work we analyze some important aspects of electrocatalyst dissolution during OER, to deepen and advance our understanding of activity‐stability relations and relevant stability descriptors.
Design of oxygen evolution reaction (OER) electrocatalysts requires development of stability descriptors, that are properties directly related to electrocatalytic rate decay and electrocatalyst material degradation rate. In this work are discussed challenges related to development of OER stability descriptors including: dissolution mechanism, reasons for structural disruption of electrocatalyst, stability vs. OER activity, importance of preexponential frequency factor for electrocatalyst dissolution etc.
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