Solar-driven dehydrogenation and dehydration of formate to syngas with near-zero CO₂ emission

Syngas, a vital H₂ and CO mixture, is crucial for industrial applications and advancing the circular carbon economy. Traditional photocatalytic CO₂ reduction to syngas relies on sacrificial agents and photosensitizers, limiting scalability and practice. Here, we demonstrate a Co₃O₄-CdS heterojunction photocatalyst that efficiently converts formate (HCOO⁻), a stable, easily-handled and accessible CO₂ reduction product, into syngas under alkaline conditions (pH ∼ 10). This dual-function catalyst enables CO generation via CdS-mediated dehydration and H₂ production via Co₃O₄-mediated dehydrogenation, achieving a syngas production rate of ∼3300 μmol g⁻¹ h⁻¹. Notably, this system operates without sacrificial agents or noble metals, with near-zero CO₂ emissions, surpassing current efficiency benchmarks. By recycling CO₂ into formic acid and further converting it to syngas, this approach promotes a closed carbon loop. Its cost-effectiveness, ease of formate storage, direct solar utilization, and low carbon footprint position it as a promising pathway for sustainable syngas production and clean energy solutions.