Tailored Sustainable Synthesis of MoxC by Electrochemical Etching of Mo2TiAlC2 MAX Phase toward Electrochemical Application

Abstract

Molybdenum carbide stands out as a promising material for energy-related applications, particularly as a hydrogen evolution reaction (HER) catalyst and a supercapacitor electrode material. However, traditional synthesis methods for molybdenum carbide are often complex, requiring multi-steps or severe conditions, which result in limited material accessibility and scalability. Herein, the work proposes a novel method for preparing molybdenum carbide materials with excellent HER catalytic performance and efficient SC capabilities by electrochemically etching the quaternary carbide (Mo2TiAlC2 MAX) precursor. The etching mechanism from Mo2TiAlC2 MAX to MoxC is systematically investigated by the experiment and the density functional theory (DFT) method. The results show that Ti and Al atoms can be completely removed by electrochemical etching in an alkaline K₂S solution. The resulting molybdenum carbide (MoxC) nanosheets exhibits remarkable HER catalytic activity due to its abundant metal vacancy defect structure. Especially, the MoxC delivers improved overpotentials (157 mV at 10 mA cm−2) in 0.5 M H2SO4 compared to Mo2TiAlC2. Theoretical calculations unraveled that MoxC exhibited a reduced Gibbs free energy for the HER. The MoxC demonstrates as an optimal candidate for supercapacitor (SC) applications, exhibiting a high specific capacitance of 394 F g⁻¹ at 2 mV s⁻¹ and excellent cycling stability, retaining nearly 94.7% of its initial capacity after 5000 cycles. The as-fabricated asymmetric supercapacitor exhibits maximum energy density of 12.4 Wh kg-1 at a power density of 89.1 W kg-1 and the capacity retention rate can still up to 80.2% even after 6000 cycles at a current density of 1 A g−1.