One of the key challenges that hinders broad commercialization of proton exchange membrane fuel cells is the high cost and inadequate performance of the catalysts for oxygen reduction reaction (ORR)....

Mixed transition‐metals (TM) based catalysts have shown huge promise for water splitting. Conventional synthesis of nanomaterials is strongly constrained by room‐temperature equilibria and Ostwald ripening. Ultra‐fast temperature cycling enables the synthesis of metastable metallic phases of high entropy alloy nanoparticles, which later transform to oxide/hydroxide nanoparticles upon use in aqueous electrolytes. Herein, an in situ synthesis of non‐noble metal high entropy oxide (HEO) catalysts on carbon fibers by rapid Joule heating and quenching is reported. Different compositions of ternary to senary (FeNiCoCrMnV) HEO nanoparticles show higher activity towards catalyzing the oxygen evolution reaction (OER) compared to a noble metal IrO2 catalyst. The synthesized HEO also show two orders of magnitude higher stability than IrO2, due to stronger carbide‐mediated intimacy with the substrate, activated through the OER process. Alloying elements Cr, Mn and V affect OER activity by promoting different oxidation states of the catalytically active TM (Fe, Ni and Co). Dissolution of less stable elements (Mn, V and Cr) leads to enhancements of OER activity. Dynamic structural and chemical perturbations of HEO oxide nanoparticles activate under OER conditions, leading to enlargement in ECSA by forming mixed single atom catalysts and ultra‐fine oxyhydroxide nanoparticles HEOs.

In this study, we explore the dimensional aspect of structure-driven surface properties of metal monolayers grown on a graphene/Au template. Here, surface limited redox replacement (SLRR) is used to provide precise layer-by-layer growth of Pt monolayers on graphene. We find that after a few iterations of SLRR, fully wetted 4-5 monolayer Pt films can be grown on graphene. Incorporating graphene at the Pt-Au interface modifies the growth mechanism, charge transfers, equilibrium interatomic distances, and associated strain of the synthesized Pt monolayers. We find that a single layer of sandwiched graphene is able to induce a 3.5% compressive strain on the Pt adlayer grown on it, and as a result, catalytic activity is increased due to a greater areal density of the Pt layers beyond face-centered-cubic close packing. At the same time, the sandwiched graphene does not obstruct vicinity effects of near-surface electron exchange between the substrate Au and adlayers Pt. X-ray photoelectron spectroscopy (XPS) and extended X-ray absorption fine structure (EXAFS) techniques are used to examine charge mediation across the Pt-graphene-Au junction and the local atomic arrangement as a function of the Pt adlayer dimension. Cyclic voltammetry (CV) and the oxygen reduction reaction (ORR) are used as probes to examine the electrochemically active area of Pt monolayers and catalyst activity, respectively. Results show that the inserted graphene monolayer results in increased activity for the Pt due to a graphene-induced compressive strain, as well as a higher resistance against loss of the catalytically active Pt surface.

Revolutionary catalyst protection by single layer graphene capping, tremendous catalyst lifetime longevity and activity enhancement towards oxygen reduction reaction.