Surface engineered MXene with multi-electroactive sites for developing durable and efficient water-splitting electrolyzer

Combining multilayered structure, tunable physicochemical, and surficial properties, two-dimensional Ti3C2Tx MXene has been extensively investigated for their potential in field of noble-metal free electrocatalysis. However, easy aggregation of MXene nanosheets and their thermodynamic instability drastically reduce active sites and, hence, decline overall water-splitting efficiency. In this regard, approaches of surface engineering of MXene by introducing large-sized dopants have been acknowledged to overcome aforementioned issues. Considering this, herein, we have proposed a strategy for tuning MXene surface by substitutional vanadium doping, which induced additional accessible electrochemically active surface sites (V0+, V1+/2+, V3+, V4+, and V5+), along with inherent MXene sites (Ti2+, Ti3+, and Ti4+). This also inhibited inevitable self-restacking with minimal inherent aqueous oxidation. Vanadium doping has created abundant intimate heterointerface networks favoring electronic redistribution on conducting surface of MXene, thereby resulting in highly active sites, predominantly with low-valence (V0+ and Ti2+) and high-valence (V5+ and Ti4+) for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively. Benefitting from surficial synergistic features, optimized sample revealed superior bifunctionality along with long-term durability to drive both HER and OER with overpotentials of 78 and 175 mV. Also, an assembled water-splitting system revealed a low cell voltage of 1.48 V. Thus, this work provides significant insight to significantly and synchronously enhance surface utilization of MXene with abundant electrochemical active sites, crucial for designing high-performance water-splitting electrolyzer.