Hierarchically Porous Nickel Stainless Steel Electrodes for Simultaneous Hydrogen and Formate Production via Membrane-Less Glucose Electrolysis

Membrane-less electrolyzers (MLEs) offer a cost-effective route to hydrogen production by eliminating membrane-related losses but are often limited by oxygen evolution reactions (OERs) at the anode. Here, we demonstrate an MLE that couples hydrogen evolution reactions (HERs) with glucose oxidation reactions (GORs) using a hierarchically porous nickel-coated stainless-steel electrode (Ni@SS) fabricated via the dynamic hydrogen bubble templating method. It delivers a much lower GOR onset potential (∼1.1 V vs RHE) than the OER, high stability, and product selectivity toward formate, achieving up to 94% formate faradaic efficiency and ∼95% glucose conversion during the 12 h long chronoamperometry study at 1.5 V (V vs RHE). In situ Raman spectroscopy reveals that the GOR proceeds via a dual-pathway mechanism involving direct oxidation on Ni(OH)2 at lower potentials and an indirect NiOOH-mediated route at higher potentials, where transient NiOOH species are rapidly reduced by glucose. This process suppresses NiOOH accumulation and effectively inhibits the OER, as confirmed by operando O2 detection below 1.55 V (vs RHE). A proof of concept using a flow cell MLE was demonstrated for glucose electrolysis, where Ni@SS bifunctional electrodes sustain 150 mA cm−2 at a cell potential below 2.0 V for over 12 h without detectable oxygen evolution. This work thereby establishes a practical strategy for integrating biomass valorization with membrane-less, high-purity H2 generation alongside value-added formate synthesis.