The Positive Effects of Carbon-Coating Layers on Protecting the Nanoparticle Towards Poisoning Ions or Gases

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Recently, the research that explores the positive effects of carbon-coating nanoparticles to fight the severe oxidation/corrosion in Alkaline fuel cell (AFC), Proton-exchange membrane fuel cell (PEMFC) or water electrolyzer is well-recognized, since the carbon layers can extend the catalyst’s durability towards hydrogen oxidation/evolution reactions (HOR, HER) and oxygen evolution/reduction reactions (OER, ORR). Especially for the reactions in alkaline pH, with the graphite coating, the Ni nanoparticles in both HOR and HER can resist passivation and hydride poisoning. [1,2] Similarly, in the same alkaline conditions, the amorphous carbon coating slows down the degradation of Pd catalysts.[3] Moreover, the coating can block big ions such as halide, thus benefiting Pt group metals from resisting halide adsorption, that eventually prevents the dissolution of metal.[4,5]In this work, we examined the gas poisoning effects on coated catalysts. For example, we synthesized carbon-coated Pd-Ni nanoparticles, supported on Vulcan carbon and studied its electrochemical response in 0.1M KOH at room temperature and its tolerance towards CO gas. As a result, Pd-Ni coated had better resistance to passivation compared to the non-coated Pd-Ni catalyst. It also showed that the thickness of the carbon coating layers was sufficient to block the CO absorption in RDE condition initially (Figure 1, black solid line). Only after 150 cycles of accelerated stress test in Ar (AST-Ar, using potential stepping between 0.1 and 1.23 V vs. RHE with a pulse of 3 s at each potential in Ar-saturated electrolyte, 6s/cycles), the passivation that occurred at high potential could cause a small portion of Pd to be “exposed” and adsorb CO (Figure 1, red solid line). After another 150 cycles of AST-Ar (AST 300), more Pd was exposed to CO adsorption but not fully. This proves the carbon-coating layers can protect the nanoparticles from poison contaminant gas such as NOx, SOx, CO, or the COx-like species. Both AFC and PEMFC systems can benefit from this type of catalyst to operate extensively without losing catalytic activity to passivation or pollution issues.