Engineering Bio-Derived Carbon Dot Mediators for Sustainable Steering of Proton-Coupled Electron Transfer in Water Oxidation.

The kinetic decoupling of proton and electron transfer during the oxygen evolution reaction (OER) represents a fundamental bottleneck in artificial photosynthesis, leading to high overpotentials and catalyst degradation. Inspired by the proton-relay function of the hydrogen-bond network in photosystem II, we report a sustainable strategy to engineer an artificial proton-transfer pathway on CoFe layered double hydroxide (LDH) electrocatalysts using vancomycin-derived carbon dots (Van-Cdots). The Van-Cdots create an extended interfacial hydrogen-bond network that actively steers the proton-coupled electron transfer (PCET) mechanism. Kinetic isotope effect measurements reveal a striking transition from a primary KIE (2.00) for pristine CoFe-LDH to a secondary KIE (≤1.49) for the Van-Cdots/CoFe-LDH hybrid, definitively removing proton transfer from the rate-determining step. pH-dependent kinetics demonstrate a shift from a concerted PCET pathway to a non-concerted mechanism, with fractional reaction orders (0.20-0.58) indicative of Grotthuss-type proton hopping. Proton inventory studies provide quantitative evidence for participation of multiple protonic sites (Z = 2.508) with an exceptionally low fractionation factor (φ = 0.076), characteristic of low-barrier hydrogen bonds approaching those inferred in natural photosynthesis. Gerischer impedance spectroscopy confirms that proton-exchange kinetics outpace natural diffusion, establishing a chemical-electrochemical-chemical mechanism. The optimized hybrid achieves a substantially reduced Tafel slope (146 mV dec-1) and enhanced stability. This work establishes bio-derived carbon dots as a sustainable, integrable platform for engineering proton-relay interfaces, bridging a critical gap between synthetic electrocatalysis and nature's integrated design.