Interface Engineering via Ti3C2Tx MXene Enabled Highly Efficient Bifunctional NiCoP Array Catalysts for Alkaline Water Splitting.

Developing a non-noble metal-based bifunctional electrocatalyst with high efficiency and stability for overall water splitting is desirable for renewable energy systems. We developed a novel method to fabricate a heterostructured electrocatalyst, comprising a NiCoP nanoneedle array grown on Ti3C2Tx MXene-coated Ni foam (NCP-MX/NF) using a dip-coating hydrothermal method, followed by phosphorization. Due to the abundance of active sites, enhanced electronic kinetics, and sufficient electrolyte accessibility resulting from the synergistic effects of NCP and MXene, NCP-MX/NF bifunctional alkaline catalysts afford superb electrocatalytic performance, with a low overpotential (72 mV at 10 mA cm-2 for HER and 303 mV at 50 mA cm-2 for OER), a low Tafel slope (49.2 mV dec-1 for HER and 69.5 mV dec-1 for OER), and long-term stability. Moreover, the overall water splitting performance of NCP-MX/NF, which requires potentials as low as 1.54 and 1.76 V at a current density of 10 and 50 mA cm-2, respectively, exceeded the performance of the Pt/C∥IrO2 couple in terms of overall water splitting. Density functional theory (DFT) calculations for the NCP/Ti3C2O2 interface model predicted the catalytic contribution to interfacial formation by analyzing the electronic redistribution at the interface. This contribution was also evaluated by calculating the adsorption energetics of the descriptor molecules (H2O and the H and OER intermediates).

Three-Dimensional MoS2/MXene Heterostructure Aerogel for Chemical Gas Sensors with Superior Sensitivity and Stability.

The concept of integrating diverse functional 2D materials into a heterostructure provides platforms for exploring physics that cannot be accessed in a single 2D material. Here, physically mixing two 2D materials, MXene and MoS2, followed by freeze-drying is utilized to successfully fabricate a 3D MoS2/MXene van der Waals heterostructure aerogel. The low-temperature synthetic approach effectively suppresses significant oxidation of the Ti3C2Tx MXene and results in a hierarchical and freestanding 3D heterostructure composed of high-quality MoS2 and MXene nanosheets. Functionalization of MXene with a MoS2 catalytic layer substantially improves sensitivity and long-term stability toward detection of NO2 gas, and computational studies are coupled with experimental results to elucidate that the mechanism behind enhancements in the gas-sensing properties is effective inhibition of HNO2 formation on the MXene surface, due to the presence of MoS2. Overall, this study has a great potential for expansion of applicability to other classes of two-dimensional materials as a general synthesis method, to be applied in future fields of catalysis and electronics.