Engineering Compressive Strain in Pd through Surface Reconstruction of Ag₂Se for Enhanced Formate Oxidation

Abstract

Direct formate fuel cells (DFFCs) represent a promising energy conversion technology, yet the development of highperformance anode catalysts for the formate oxidation reaction (FOR) remains challenging. Here, we report a novel strain engineering strategy that harnesses the volume contraction associated with the surface reconstruction of Se into Ag₂Se to induce compressive strain in Pd catalysts. The activated Ag₂Se-Pd hybrid catalyst exhibits exceptional FOR activity, achieving a mass activity of 3.59 A mg -1 Pd -3.55 times that of conventional AgPd and 5.79 times that of commercial Pd/Calong with superior stability. Comprehensive experimental characterization, including HRTEM, GPA strain mapping, XPS, and in situ Raman spectroscopy, reveals that the activation process involves the reconstruction of surface Ag and Se species into Ag₂Se, which generates substantial compressive strain (-2.5% ~ -3.1%) in the adjacent Pd lattice. DFT calculations demonstrate that this strain downshifts the d-band center of Pd, weakening the adsorption of both HCOO* and H* intermediates. Notably, H* adsorption-the potential rate-limiting step-is highly sensitive to strain, varying by 0.78 eV across 0 ~ -5% strain. Bader charge analysis confirms that Ag₂Se formation exerts minimal electronic perturbation on Pd, establishing strain as the primary origin of the enhanced catalysis. This work not only validates our hypothesis regarding strain-enhanced FOR activity but also establishes Ag₂Se-induced volume compression, driven by surface reconstruction, as a generalizable platform for strain engineering in heterogeneous catalysis, offering a practical design principle for developing high-performance catalysts through controlled lattice contraction.