Cobalt-Anchored Carbon Quantum Dots as Surface Cocatalysts for Enhanced Oxygen Evolution Reaction on Hematite Photoanodes

Abstract Hematite (α-Fe2O3) is a promising photoanode material for photoelectrochemical (PEC) solar water splitting because of its suitable bandgap, earth abundance and chemical stability. However, its practical application is still limited by severe charge recombination and sluggish surface water-oxidation kinetics. In this work, Co-anchored carbon quantum dots (Co-CQDs) were synthesized by the pyrolysis of citric acid and cobalt nitrate, and subsequently integrated onto the surface of α-Fe2O3 through a hydrothermal−hydrolysis process to construct Co-CQDs/α-Fe2O3 composite photoanodes. After cyclic voltammetry (CV) activation, the optimized A-Co-CQDs/α-Fe2O3 delivered a photocurrent density of 2.03 mA cm−2 at 1.23 V vs RHE, approximately 3.22 times that of bare α-Fe2O3. The enhanced PEC performance is attributed to the synergistic effect of Co-CQDs, which promote interfacial charge separation and accelerate water-oxidation kinetics. Specifically, CQDs provide a conductive network for charge transport, while Co species serve as hole-trapping and water oxidation active centers. In addition, the Co-CQDs modification increases the electrochemically active surface area and exposes more accessible active sites. Mechanistic analysis further suggests that CV activation promotes the generation of more oxidized Co species and hydroxyl-rich surface environments, which could facilitate surface hole accumulation and oxygen evolution reaction. This work provides a feasible strategy for improving the PEC performance of α-Fe2O3 photoanodes through carbon quantum dot-based surface modification and transition-metal active-site engineering.