O-terminated Ti3C2Tx supported sulfurized NiCo layered double hydroxide as efficient electrocatalyst for methanol coupled water electrolysis

Conventional electrocatalytic water electrolysis (WE) technology has long been hindered by the slow kinetics of anodic oxygen evolution reaction (OER). It is then thermodynamically more favorable to replace OER with methanol oxidation reaction (MOR), which enables lower energy consumption and higher efficiency for hydrogen production. For such emerging methanol-coupled WE systems, it is pressing to develop efficient, stable and low-cost electrocatalysts for MOR as well as hydrogen evolution reaction (HER). Herein, an O-terminated Ti3C2Tx MXene (Ti3C2Ox) supported sulfur-doped NiCo layered double hydroxide (termed NiCo-SOH/Ti3C2Ox) heterostructure is developed by termination modulation and surface sulfurization techniques. The NiCo-SOH/ Ti3C2Ox catalyst achieves an excellent MOR activity with Ej10 potential of only 1.290 V, much lower than the corresponding OER potential (1.456 V) under the same test condition, validating the significant advantage of MOR over OER. Furthermore, the Tafel slope for MOR is only 47 mV dec- 1 for NiCo-SOH/Ti3C2Ox catalyst, far surpassing that (145 mV dec- 1) for IrO2 benchmark. The electronic interaction between S2- and transition metal ions, as well as the superior conductive capability of Ti3C2Ox substrate synergistically generate highly efficient NiCo active sites and accelerate the charge transfer process, leading to high MOR activity for NiCo-SOH/Ti3C2Ox. In addition, the NiCo-SOH/Ti3C2Ox catalyst demonstrates a remarkably high stability for MOR and a good HER activity. Based on the excellent MOR/HER activity and stability of NiCo-SOH/Ti3C2Ox, the NiCo-SOH/Ti3C2Ox|| NiCo-SOH/Ti3C2Ox symmetrical methanol-water co-electrolysis cell shows a low termination voltage of only 1.389 V at 10 mA cm- 2 and excellent stability without obvious degradation, remarkably superior to the traditional water electrolyzer.