Cadmium sulfide doping enhances MXene catalyst for hydrogen production

Researchers have developed a series of cadmium sulfide-doped Ti3C2Tx MXene nanocomposites, identifying an optimal formulation for the electrocatalytic hydrogen evolution reaction (HER). This process is crucial for producing clean hydrogen fuel from water. Published in Discover Chemical Engineering, the study found that a composite with 1 wt% CdS exhibited the best catalytic performance among the materials tested.

The research team, led by Ritu Raj, Mitali Hupele, Yalamarti Venkat Rajat Rao, Rajan Singh, Krishna Kanta Haldar, and Gajendra Prasad Singh, synthesized four composites, labeled MC1 through MC4, with CdS loadings from 0.5 to 5 wt%. These materials were produced using a hydrothermal method and tested as HER catalysts in a 0.5 M H2SO4 electrolyte, a challenging acidic environment for most catalysts.

Structural analysis confirmed the successful integration of CdS into the layered MXene host. X-ray diffraction verified the doping of CdS into the MXene structure, while Raman spectroscopy showed systematic phonon shifts indicating compressive in-plane strain. Transmission electron microscopy revealed CdS nanoparticles anchored onto the Ti3C2Tx nanosheets, demonstrating close contact between the two components.

The interfacial loading was critical to performance. Among the composites, the sample with 1 wt% CdS, designated MC2, was identified as the optimal composition. This suggests that the balance between CdS coverage and MXene surface accessibility is crucial for catalytic activity.

In electrochemical tests, MC2 recorded the lowest overpotential of the series, 310 mV at a current density of -10 mA/cm2, and the smallest Tafel slope of 98 mV/dec. These results indicate that the composite requires less applied voltage for hydrogen generation and has more favorable reaction kinetics than the other samples.

MC2 also demonstrated advantageous charge-transfer properties. Electrochemical impedance measurements showed the lowest charge transfer resistance of the series at 152.2 ohms, the highest mass activity of 48.90 A/g, and the largest electrochemically active surface area of 38.625 cm2. A larger active surface area provides more sites for the hydrogen evolution reaction, contributing to the composite’s superior activity.

Durability is essential for practical electrocatalysts, and the optimized composite performed well in stability tests. MC2 maintained its activity over 2000 linear sweep voltammetry cycles, with only a negligible overpotential shift of 9.21 mV, indicating that the CdS-MXene interface remains functional under prolonged acidic conditions.

The authors suggest that CdS-doped Ti3C2Tx MXene is a promising, cost-effective electrocatalyst for sustainable hydrogen production. This aligns with the search for efficient catalysts made from earth-abundant elements rather than precious metals. As the study reports performance in laboratory electrochemical testing in 0.5 M H2SO4, further research is needed to evaluate the material's performance in operating devices and over longer periods. The findings contribute to the growing research on MXene-based and transition-metal-doped catalysts for hydrogen evolution, a field that includes recent reviews and studies on heterojunction designs combining MXenes with other two-dimensional materials.