The direct oxidation of methane (CH4) to formaldehyde (HCHO) with molecular oxygen (O2) as the sole oxidant was studied over various bismuth-based catalysts (BiPO4, α-Bi2O3, β-Bi2O3) using a fixed-bed flow...

Ambient pressure XPS is a powerful technique capable of performing measurements with samples kept at mbar pressure. The filled gas, also X‐ray ionized, provides electrons to neutralize positive charges built up on insulating samples. However, this convenient neutralization scheme does not solve the charging problem completely. In this study, the effectiveness of how the electrons generated from conducting mechanical parts mounted in the immediate front of insulating samples neutralize positive charges on the samples during XPS measurements is tested. The mechanical parts range from fine gold mesh, holey carbon film to graphene monolayer, and measured insulating samples are polished sapphire and rough pellets of CaCO3 powder. All these mechanical add‐ons reduce the charging to different degrees at the expense of sample signal. Amazingly, the graphene monolayer is found to effect perfect charge neutralization for both smooth sapphire and rough CaCO3 pellet, evidenced by realistic spectral profile and binding energy values. The finding that an untreated CaCO3 pellet is often terminated with Ca(OH)(HCO3) is consistent with earlier reports. It is speculated that a likely conformal covering with graphene on the sample with rough morphology holds the key to its superb performance in charge compensation.

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The stability and activity of Platinum catalysts under the redox process are the key parameters affecting catalytic performance. Here, we investigated the surface species evolution of low‐loading Pt catalyst deposited on a Nafion membrane through e‐beam deposition during redox reactions by using in situ X‐ray photoelectron spectroscopy (XPS) combined with a static electrochemical cell. Operando ambient‐pressure XPS measurement revealed the oxide species (Ptδ+, Pt2+, and Pt4+) evolution over different potentials in the water layer constructed by an acid solution. The amount of Pt2+ increased with an increment of the anodic potential, whereas Pt4+ suddenly formed when the threshold voltage of the oxygen evolution reaction was crossed. Hysteresis of Pt2+ was revealed as Pt4+ was completely reduced when returning to the open circuit potential. Incorporating depth‐profiling studies enabled us to uncover the mechanism of oxide species evolution between the surface and subsurface of the Pt catalyst during a redox reaction.