Engineering stable electrocatalysts by synergistic stabilization between carbide cores and Pt shells

Abstract

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

Stable and Active Oxygen Reduction Catalysts with Reduced Noble Metal Loadings through Potential Triggered Support Passivation

“…In a previous study, imperfect Pt coverages on a non‐noble core material has led to fast and quantitative dissolution of the core revealing the need for material combinations that can withstand the harsh ORR conditions . Early transition metal carbides were reported to exhibit metallic conductivity, high corrosion resistance and are able to strongly bind to noble metals such as Pt anchoring it in place .…”

Alloying–Realloying Enabled High Durability for Pt–Pd–3d-Transition Metal Nanoparticle Fuel Cell Catalysts

“…This finding is supported not only by the results from testing a series of Pt-alloy catalysts with an increase in noble metal content in this work (Supplementary Table 2), but also by results reported previously for high-Pt-content alloys starting from a low Pt content (e.g., PtNi 3 ) 5,7 . While it is feasible that a further examination of the very small percentage change of the dissolved metal ions in the RDE experiment, which is even smaller in MEA in the experimental time scale as discussed later, by ICP-OES or in-situ ICP-mass spectroscopy 36 could gain some information on the transient behavior. However, since dealloying occur mostly at the initial few tens/hundreds of potential cycles as known by the analysis of the Cu redox waves in the potential cycling ( Supplementary Fig.…”

Advances and challenges for experiment and theory for multi-electron multi-proton transfer at electrified solid–liquid interfaces

“…The complexity of model solid/liquid systems increase from Level 2 (alloying, doping, nanostructuring, or other modifications), Level 3 (addition of interfacial promotors on electrode surfaces and/or in electrolyte), 221,[440][441][442][443][444] to Level 4. [445][446][447][448][449][450][451][452][453] VESTA was used to prepare several structure images in the panel A. 454 (B) Evaluations of present level of achievement for each combination of an electrode-system complexity.…”

“…12) or much more realistic structures/morphologies. 445,446,[575][576][577][578] Of course, there are much more complicated systems, such as microbes. [579][580][581][582][583][584][585][586][587][588] These systems are so complicated that it is challenging to unveil their microscopic working principles.…”