The electrochemical production of hydrogen and hydrocarbons is considered to play a decisive role in the conversion and storage of excess amounts of renewable energy. The electrocatalysis of the oxygen evolution reaction (OER), however, faces significant challenges for practical implementation of electrolyzers. In this work, a comparative study on the activity and stability of oxidized polycrystalline noble metals during the OER is presented. All studied metals exhibit transient and steady-state dissolution. Transient dissolution takes place during oxide formation and reduction. Steady-state dissolution depends on the OER mechanism on each surface: On metals such as Ru and Au, for which oxygen from the oxide participates in the OER, the Tafel slope is low and the dissolution rate is high. In contrast, on metals for which oxygen evolves directly from adsorbed water, such as Pt and presumably Pd, the Tafel slopes are high and the dissolution rates are low. This should be considered in the design of optimal OER catalysts.The conventional energy strategy based on the deployment of fossil fuels comprises two serious drawbacks: depletion of irretrievable fuels and environmental concerns upon their exploitation. As a consequence, the growing general interest in the concept of sustainable renewable energy has boosted the implementation of alternative energy supply technologies over recent years. [1] Particularly, the utilization of energy from sun and wind is considered as an adoptable scenario in the energy paradigm shift, as each of them is capable of covering the global energy demand, which is estimated to be 17 TW in 2030. [2] Unlike traditional energy supplies, however, the production of electricity from sun and wind is intermittent, which creates a terawatt-scale challenge: fluctuations in energy supply by variation of seasonal weather conditions must be efficiently leveled off. Consequently, besides production itself, conversion and storage of enormous amounts of energy during peak production hours as well as its constant distribution to end users during downtime is an essential piece of the puzzle. One approach capable of handling the terawatt scale is the conversion of electrical energy and storage in the form of chemical bonds as, for example, hydrogen (through water reduction) or hydrocarbons (through carbon dioxide reduction). [3] For instance, these fuels can be produced electrochemically in electrolyzers [4] and then utilized at local fuel cell factories or transported to consumers on demand. [5] The essential counterreaction in an electrolyzer for either technology (water or CO 2 reduction) will be the oxygen evolution reaction (OER). However, the high energy required for the rearrangement of the chemical bonds of water during the OER is actually a bottleneck in the production costs compared to other technologies such as reforming. [3a, 6] Namely, sluggish electrode kinetics and detachment of evolved gas bubbles can severely restrict efficiency. [7] Moreover, the catalyst activity needs to be sustained...
One of the most important practical issues in low‐temperature fuel‐cell catalyst degradation is platinum dissolution. According to the literature, it initiates at 0.6–0.9 VRHE, whereas previous time‐ and potential‐resolved inductively coupled plasma mass spectrometry (ICP–MS) experiments, however, revealed dissolution onset at only 1.05 VRHE. In this manuscript, the apparent discrepancy is addressed by investigating bulk and nanoparticulated catalysts. It is shown that, given enough time for accumulation, traces of platinum can be detected at potentials as low as 0.85 VRHE. At these low potentials, anodic dissolution is the dominant process, whereas, at more positive potentials, more platinum dissolves during the oxide reduction after accumulation. Interestingly, the potential and time dissolution dependence is similar for both types of electrode. Dissolution processes are discussed with relevance to fuel‐cell operation and plausible dissolution mechanisms are considered.
Pt dissolution has already been intensively studied in aqueous model systems and many mechanistic insights have been gained. Nevertheless,t ransfer of new knowledge to realworld fuel cell systems is still as ignificant challenge.T oc lose this gap,w ep resent an ovel in situ method combining ag as diffusion electrode (GDE) half-cell with inductively coupled plasma mass spectrometry (ICP-MS). With this setup,P t dissolution in realistic catalyst layers and the transport of dissolved Pt species through Nafion membranes were evaluated directly.W eo bserved that 1) specific Pt dissolution increased significantly with decreasing Pt loading, 2) in comparison to experiments on aqueous model systems with flowc ells,t he measured dissolution in GDE experiments was considerably lower,a nd 3) by adding am embrane onto the catalyst layer,Ptdissolution was reduced even further.All these phenomena are attributed to the varying mass transport conditions of dissolved Pt species,i nfluencing re-deposition and equilibrium potential.
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