A dual-active Co-CoO heterojunction coupled with Ti3C2-MXene for highly-performance overall water splitting

Development of cost-effective and highly-efficient bifunctional hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) catalysts is crucial for overall water splitting in practical utilization. Herein, we proposed a novel non-noble metal bifunctional HER/OER electrocatalyst by synergistically coupling a dual-active Co-based heterojunction (Co-CoO) with high conductive and stable two-dimensional Ti3C2-MXene (defined as Co-CoO/Ti3C2-MXene). A series of characterizations and theoretical calculations verify that the synergistic effect of metallic Co with HER activity and CoO with OER performance leads to superb bifunctional catalytic performance, and Ti3C2-MXene can enhance electrical conductivity and prevent the aggregation of the Co-based catalysts, thereby improving both the activity and stability. Co-CoO/Ti3C2-MXene presents low onset potential (ηonset) of 8 mV and Tafel slope of 47 mV·dec−1 for HER (close to that of Pt/C) and ηonset of 196 mV and Tafel slope of 47 mV·dec−1 for OER (superior to that of RuO2). Assembled as an electrolyzer, Co-CoO/Ti3C2-MXene shows a low voltage of 1.55 V at 10 mA·cm−2, high Faradaic efficiency and remarkable stability. It can be driven by a solar cell of ∼ 1.55 V for consecutive production of hydrogen and oxygen gases.