Mechanism-Guided Selectivity and Bifunctionality in Glycerol Electrooxidation on Ag-Based Transition-Metal Single-Atom Alloys

Electrocatalytic glycerol oxidation reaction (GOR) offers a promising route for upgrading biomass-derived molecules to value-added chemicals and fuels. However, achieving high catalytic activity and product selectivity remains a significant challenge, requiring a comprehensive understanding of the underlying reaction mechanism. In this study, we systematically investigate a series of transition-metal single-atom-doped Ag(111) catalysts (TM1Ag, TM = Pd, Pt, Au, Cu, Ru, Rh, and Ir), selected based on electrochemical stability criteria including like Pourbaix diagrams. Two glycerol (GLY) adsorption configurations (GLYup* and GLYdn*) are selectively converted to glyceraldehyde and dihydroxyacetone via four pathways (Paths a–d), with reactions initiated by O–H activation (Paths a and c) favored over C–H activation (Paths b and d), followed by subsequent oxidation steps (Paths I–X). The calculated activity trend follows the order: Ru1Ag > Rh1Ag > Pt1Ag ≈ Ir1Ag > Pd1Ag > Au1Ag > Ag(111) > Cu1Ag. To rationalize the performance differences, we propose two intrinsic descriptors─the ratio of valence electron count to electronegativity (ZVAL/X) and the atomic radius (rTM) that effectively correlate with the overall GOR activity. Notably, TM1Ag catalysts with TM = Ru, Rh, Pt, Ir, or Pd exhibit enhanced selectivity toward glycolic acid (GCA). Importantly, all selected catalysts effectively suppress the competing oxygen evolution reaction. Furthermore, Pd1Ag and Pt1Ag demonstrate good bifunctional performance, concurrently facilitating anodic GOR toward GCA and the cathodic hydrogen evolution reaction to generate H2. This work provides mechanistic insights design principles for developing high-performance electrocatalysts for biomass valorization.