Upconversion-Assisted Solar-Driven Hydrogen Evolution in β-SiC via Synergistic Upconversion-Polydopamine Integration...

The inability of conventional photocatalysts (such as CdS, TiO₂, β-SiC, etc.) to absorb sub-band gap photons remains a significant barrier to the efficient conversion of solar energy into hydrogen energy. Herein, specifically to address this issue, we developed an efficient photocatalyst by utilizing an upconversion (UC) strategy. In this work, we synthesized an UC material, YAlO₃ doped with holmium (Ho³⁺) and erbium (Er³⁺) ions (UC-50) and then integrated it with β-SiC to form a composite nanosystem (β-SiC@UC-50). The composite nanosystem was further surface functionalized by coating it with a thin polydopamine (PDA) layer (β-SiC@UC-50_PDA). PDA improves dispersibility, facilitates widespread photon absorption, and offers a conductive surface for electron transport. The photocatalytic (PC) and photoelectrocatalytic (PEC) assessments were conducted in 0.1M Na₂S/Na₂SO₃ electrolyte. The synergistic integration of both components significantly enhances the PC performance of β-SiC. The β-SiC@UC-50 composite produced 3.9-fold more H₂ than pristine β-SiC, whereas β-SiC@UC-50_PDA further improved activity, generating 4.6-fold higher H₂ under visible light with excellent stability. β-SiC@UC-50_PDA also achieved an apparent quantum efficiency of 11.53% at 650 nm and delivered a transient photocurrent nearly 2.9-fold greater than β-SiC at 1.7 V RHE, indicating superior charge separation. In situ electrochemical analysis using a Pt interdigitated electrode confirmed elemental sulphur formation from S^2- photooxidation. Additionally, integrating a thermoelectric generator enabled efficient conversion of excess heat into electrical energy, improving overall energy utilization. This work demonstrates a multifunctional strategy to boost hydrogen production in β-SiC by combining an UC material (YAlO₃:Ho³⁺/Er³⁺), conductive PDA, and thermoelectric harvesting.