The reduction in noble metal content for efficient oxygen evolution catalysis is a crucial aspect towards the large scale commercialisation of polymer electrolyte membrane electrolyzers. Since catalytic stability and activity are inversely related, long service lifetime still demands large amounts of low-abundant and expensive iridium. In this manuscript we elaborate on the concept of maximizing the utilisation of iridium for the oxygen evolution reaction. By combining different tin oxide based support materials with liquid atomic layer deposition of iridium oxide, new possibilities are opened up to grow thin layers of iridium oxide with tuneable noble metal amounts. In-situ, time-and potential-resolved dissolution experiments reveal how the stability of the substrate and the catalyst layer thickness directly affect the activity and stability of deposited iridium oxide. Based on our results, we elaborate on strategies how to obtain stable and active catalysts with maximized iridium utilisation for the oxygen evolution reaction and demonstrate how the activity and durability can be tailored correspondingly. Our results highlight the potential of utilizing thin noble metal films with earth abundant support materials for future catalytic applications in the energy sector.

A fundamental understanding of the behavior of non-noble based materials toward the hydrogen evolution reaction is crucial for the successful implementation into practical devices. Through the implementation of a highly sensitive inductively coupled plasma mass spectrometer coupled to a scanning flow cell, the activity and stability of non-noble electrocatalysts is presented. The studied catalysts comprise a range of compositions, including metal carbides (WC), sulfides (MoS ), phosphides (Ni P , Co P), and their base metals (W, Ni, Mo, Co); their activity, stability, and degradation behavior was elaborated and compared to the state-of-the-art catalyst platinum. The non-noble materials are stable at HER potentials but dissolve substantially when no current is flowing. Through pre- and post-characterization of the catalysts, explanations of their stability (thermodynamics and kinetics) are discussed, challenges for the application in real devices are analyzed, and strategies for circumventing dissolution are suggested. The precise correlation of metal dissolution with applied potential/current density allows for narrowing down suitable material choices as replacement for precious group metals as for example, platinum and opens up new ways in finding cost-efficient, active, and stable new-generation electrocatalysts.

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Core-shell particles with earth-abundant cores represent an effective design strategy for improving the performance of noble metal catalysts, while simultaneously reducing the content of expensive noble metals 1-4. However, the structural and catalytic stabilities of these materials often suffer during the harsh conditions encountered in important reactions, such as the oxygen reduction reaction (ORR) 3-5. Here, we demonstrate that atomically thin Pt shells stabilize titanium tungsten carbide cores, even at highly oxidizing potentials. In situ, timeresolved experiments showed how the Pt coating protects the normally labile core against oxidation and dissolution, and detailed microscopy studies revealed the dynamics of partially and fully coated core-shell nanoparticles during potential cycling. Particles with complete Pt coverage precisely maintained their core-shell structure and atomic composition during accelerated electrochemical ageing studies consisting of over 10,000 potential cycles. The exceptional durability of fully coated materials highlights the potential of core-shell architectures using earth-abundant transition metal carbide (TMC) and nitride (TMN) cores for future catalytic applications. The development of core-shell nanostructures with controllable size, shell thickness, surface facets and composition vastly expands the possibility for engineering noble metal catalysts with enhanced performance 4. Numerous core-shell systems have been synthesized for catalytic applications, very often with other noble metal cores, such as Ru (refs. 6,7), Pd (refs. 5,8), Ag (ref. 9) and Ir (ref. 10) with marginal cost benefits. Critically, these core-shell materials along with those comprising earth-abundant, metallic cores (for example, Fe, Co and Ni) form intrinsically metastable structures with miscible core and shell elements that degenerate during electrochemical cycling or annealing due to metal leaching or migration 5,7,8,11. These instabilities result in considerable losses in active surface area and performance over time, imposing major barriers for the broad usage of core-shell architectures in industrial applications, where stability is essential. This is especially true for fuel cell technologies, the commercialization of which has been hindered by the poor durability of ORR catalysts 3,12-14. Early TMCs and TMNs are ideal core materials due to their thermal and chemical stability, electrical conductivity, low cost and intrinsic ability to bind strongly to noble metals while still being immiscible with them 15,16. Unfortunately, the formation of surface oxides or carbon on TMCs and TMNs presents a difficult synthetic