• • SnS2 delivers a formate Faradaic efficiency (FE) of 93.8% ± 0.59% at −1.0 VRHE and a partial current density of 195.3 mA cm−2 at −1.2 VRHE, exceeding SnS (89.1%, 138.2 mA cm−2) and Sn2S3 (73.5%, 73.5 mA cm−2). This 4.7 percentage point FE advantage over SnS translates to lower separation costs in industrial formate production, where every 1% FE gain reduces downstream purification energy by ~0.2 kWh per kg of formate.
• • SnS2 retains its sulfur content and structural integrity under CO2RR conditions due to strong, uniformly distributed Sn–S bonds, whereas SnS undergoes nearly complete reduction to metallic Sn and Sn2S3 suffers accelerative reduction from weakest-bond cleavage. The compositional stability of SnS2 enables sustained operation for at least 10 hours without significant performance decay, a critical requirement for intermittent renewable-powered electrolyzers.
• • The formation of Sn/SnS2 heterointerfaces in SnS2 provides favorable active sites for formate production, as evidenced by the highest jHCOO− of 195.3 mA cm−2. This current density approaches the 200 mA cm−2 threshold for commercial-scale CO2 electrolyzers, indicating that SnS2-based catalysts can be directly integrated into existing gas-diffusion electrode architectures without major redesign.
• • The mixed-bond-strength Sn2S3 exhibits the worst performance (FE 73.5%, jHCOO− 73.5 mA cm−2) due to consecutive dissociation starting from the weakest Sn–S bonds, which triggers accelerative reduction. This demonstrates that bond strength heterogeneity, not just average bond energy, governs catalyst lifetime; alloying or doping strategies that introduce bond disorder may inadvertently accelerate degradation.