Direct Z-scheme SiNWs@Co₃O₄ photocathode with a cocatalyst of sludge-derived carbon quantum dots for efficient photoelectrochemical hydrogen production

Solar driven photoelectrochemical (PEC) hydrogen production has attracted considerable attention, but the design of highly efficient, robust and low-cost photocathode still remains a significant challenge. Herein, we report a novel SiNWs@Co₃O₄ Z-scheme heterojunction photocathode with carbon quantum dots eco-friendly derived from sludge (SCQDs) as the co-catalyst. The photocathode not only leads to effective separation of electron–hole pair, lower transmission resistance, and longer lifetime of charge carriers, but also elevates the stability by preventing direct contact between the SiNWs and the electrolyte as well as the self-oxidation. Simultaneously, the excellent electron transport properties of the SCQDs further improved the PEC performance. Correspondingly, a maximum current density of 14.88 mA·cm⁻² was obtained at −0.67 V with the applied bias photon-to-current efficiency (ABPE) achieving 8.4% under visible light irradiations at pH = 7. This work provides a promising scheme for Si-based photocathodes for PEC hydrogen production with a high performance, reliable stability, and low-cost.