Molecular Weight Engineering Modulates Lignin-Metal Supramolecular Framework to Construct Carbon-Coated CoRu Alloy for Effective Overall Water Splitting

Abstract

To overcome the challenges of low catalytic activity and instability, a molecular weight engineering strategy coupled with oxidative ammonolysis is developed to synthesize CoRu-based alloy catalysts with distinct morphologies and properties from biorefinery lignin. This approach effectively modulates intrinsic active sites and exposes unsaturated nitrogen-oxygen structures, thereby tailoring the morphology and defect structure of the carbon layers in the catalysts. The as-synthesized CoRu alloy catalysts from lignin precursors with varying molecular weights are designated as CoRu@OALC-EtOAC, CoRu@OALC-EtOH, and CoRu@OALC-Residual. CoRu@OALC-EtOAC, featuring a defect-rich graphitic carbon-coated CoRu alloy structure, exhibited exceptional overall water-splitting performance (1.48 V at 10 mA cm⁻²), significantly surpassing Pt/C || Ru/C (1.58 V at 10 mA cm⁻²). In contrast, CoRu@OALC-Residual, with its amorphous carbon-coated CoRu alloy structure, demonstrated remarkable stability (350 h at 100 mA cm⁻²), vastly outperforming Pt/C || Ru/C (6 h at 100 mA cm⁻²). In-situ Raman spectroscopy and DFT calculations revealed that the defect-rich carbon layers effectively adsorb ^*H intermediates, accelerating the catalytic process. This strong adsorption also induces carbon layer rearrangement, leading to its dissolution of the carbon layer and oxidation of CoRu metal particles. This strategy provides a universal method for biomass-derived catalysts, establishing a direct relationship between molecular weight, catalyst morphology, and electrocatalytic performance.