CuS nanoparticle/TiO2 nanosheets heterojuncture boosting paired electrosynthesis of formate

•CuS/TiO2 nanosheets bifunctional catalysts were designed.•The heterojunctions boost both CO2RR and MOR toward formate.•A total FE formate of 168.7 % at 10 mA cm−2 was achieved by paired electrosynthesis. There is still a gap in research on the use of TiO2 as a multiphase catalyst for electrocatalysis. This paper explores the boosting effect of TiO2 nanosheets (NSs) in CuS/TiO2 NSs bifunctional catalysts which enhances their electrocatalytic formate production in both anodic methanol oxidation reaction (MOR) and cathodic carbon dioxide reduction reaction (CO2R). The boosting effect of TiO2 nanosheet is ascribed to the in-built CuS/TiO2 heterojunctions which have abundant heterointerface boundaries, adjusted electrolyte/catalyst environment, improved electrochemical active area as well as facile electron transfer. The cathodic CO2RR with CuS/TiO2 NSs showed a formate Faraday efficiency (FE formate) of 75 % at −0.9 V (vs. RHE), while the anodic MOR exhibited 97 % FE formate at 1.7 V (vs. RHE). Particularly, paired electrolysis of formate was realized in an H-type cell through simultaneous cathodic CO2RR and anodic MOR, achieving a total FE formate of 168.7 % at 10 mA cm−2.