Janus heterostructure of cobalt and iron oxide as dual-functional electrocatalysts for overall water splitting

In electrocatalytic water splitting, low-cost dual-functional catalysts can not only reduce costs but also avoid cross-contamination of cathode and anode. However, the orderly aggregation of active sites for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) into a specific catalyst is very challenging. In this study, a Co/Fe₃O₄ Janus heterojunction supported on carbon fiber paper (J-CoFe-CFP) is designed and successfully synthesized. Generally, Co-Fe oxides have preferable OER activity but weak HER activity. However, in J-CoFe-CFP, due to the intense and special electronic interaction of different substances (Co and Fe₃O₄) in the Janus heterogeneous interface, a huge number of tidy high-quality HER and OER active sites are uniformly distributed on the interface simultaneously, which endows the catalyst with both excellent HER and OER performance. In HER, the overpotential @10 mA·cm⁻² (η_HER) is only 53.9 mV, and the Tafel slope is 43.7 mV·dec⁻¹. In OER, the η is 272 mV, and the Tafel slope is 50.2 mV·dec⁻¹, much lower than those of RuO₂/CFP. In the J-CoFe-CFP||J-CoFe-CFP two-electrode system, the required voltage is only 1.26 V at the beginning and 1.56 V@10 mA·cm⁻², much lower than those of RuO₂/CFP||20% Pt/C/CFP. This work provides a Janus heterojunction pathway for bifunctional water electrolysis catalysts.