Remarkably enhanced catalytic activity by the synergistic effect of palladium single atoms and palladium–cobalt phosphide nanoparticles

For the realization of commercially viable ethanol fuel cells, despite much safer than hydrogen gas, it is necessary to develop stable high-performance catalysts for ethanol electro-oxidation reaction (EOR). Unfortunately, current EOR catalysts are far from the expectation and suffer from fast activity degradation. Here we report palladium-cobalt phosphide (Pd–Co₂P) nanoparticles (NPs) with Pd single atoms (PdSAs) anchored on graphene oxide (GO) (denoted as Pd–Co₂P–PdSAs@GO). Its EOR mass activity (10,520 mA/mg_Pd) is remarkably larger than any reported carbon-based precious metal catalysts including the benchmark Pd/C catalyst. To achieve high activity and stability, we systematically designed the catalyst with optimized elements ratio (Pd, Co/Ni/Fe, and P) and pyrolysis temperature together with electrochemical activation. The synergistic effect of charge-transfer between Pd and Co₂P coexisting on the PdSAs@GO surface to shift the Pd d-band center promotes the bimetallic catalyst activity. The strong binding of PdSAs@GO with metals and the phosphide ligand stabilized NPs provide long-term durability. In-situ Raman analysis reveals that Co₂P plays major roles in eliminating poisoning CO at neighboring Pd sites and retaining the catalytic activity even after 20 h.