Single-Layer Narrow-Bandgap Co-Doped Ti₂CO₂ MXene as a Multifunctional Cocatalyst for Scalable and Stable BiVO₄...

Bismuth vanadate (BiVO₄) is a promising candidate for photoelectrochemical (PEC) water splitting, yet its performance is limited by sluggish oxygen evolution reaction (OER) kinetics. Although oxygen evolution cocatalysts (OECs) mitigate this issue, conventional OEC systems often require additional hole-transport layers to form multilayer cascade architectures, which inevitably increase interfacial resistance and hinder scalable fabrication. Herein, we simplify the photoanode design by developing a single-layer, multifunctional OEC based on Co-doped Ti₂CO₂ quantum dots for BiVO₄ photoanodes (Co:Ti₂CO₂/BiVO₄). The optimized photoanode achieves a remarkable photocurrent density of 4.48 mA·cm^-2·for water oxidation, which further reaches 6.24 mA·cm^-2 (83.2% of the theoretical limit) in the presence of a hole scavenger at 1.23 V versus reversible hydrogen electrode. Meanwhile, it exhibits excellent photocorrosion resistance for over 130 h. The performance enhancement arises from the synergistic effect of the Co-doped Ti₂CO₂ layer. Its narrow-bandgap semiconducting Ti₂CO₂ skeleton acts as a fast channel to suppress charge recombination, while Co dopants provide active sites to promote surface OER kinetics. Additionally, a large-area photoanode of 100 cm² was successfully fabricated using the same scalable all-spray pyrolysis approach, underscoring its potential for practical deployment. This work offers new insights into the development of cost-effective, scalable, and efficient PEC devices.