Optimization of strain-correlated electronic modulation and interfacial microenvironment for oxide-shielded PdGa nanosheets toward bifunctional electrocatalysis.

A critical challenge hindering the commercial application of direct methanol fuel cells (DMFCs) as highly promising energy conversion devices lies in the CO intermediates strongly adsorbed on catalyst surfaces leading to catalyst poisoning. Herein, PdGa alloy nanosheets (NSs) bounded by amorphous GaO atomic layers were constructed by utilizing strong p-d orbital coupling and tensile lattice strain. The PdGa NSs attain the exceptional methanol oxidation reaction (MOR) and oxygen reduction reaction (ORR) mass activities of 1.18 A mg and 1.23 A mg, respectively, 11.80-fold and 17.57-fold enhanced relative to those of Pd/C. A superb 86% of the initial MOR activity was retained after a long chronoamperometric test of 10,000 s. More importantly, multiple in-situ spectroscopic characterizations demonstrate that strong p-d orbital coupling serves to circumvent CO poisoning due to electron localization around Pd, and that tensile strain is beneficial for stabilization of formate intermediates toward non-CO pathway, which is also facilitated by the optimized interfacial water modes for PdGa NSs. Meanwhile, the thin yet stable GaO protective layers restrain metallic dissolution with unaffected exposure of active sites such as high-index facets. The strategy has been extended to PdIn NSs with InO atomic layers and this work opens up a new route for advanced design of bifunctional electrocatalysts for DMFCs.