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Tremendous enthusiasm for bi-atom catalysts (BACs) for the nitrogen reduction reaction (NRR) has been aroused due to the insufficient activation of N2 in single-atom catalysts (SACs). Herein, using density functional theory (DFT) calculations, the catalytic activities toward NRR of the NbS2-based SACs and BACs have been investigated. Our results reveal that there are typical volcano relationships between catalytic activities (limiting potentials) and the adsorption free energies of NNH* (∆G(NNH)*) on SACs, but the peak limiting potential is only −0.57 V. Interestingly, this volcano relationship can be reconstructed by supporting bi-atoms sites on NbS2, in which ∆G(NH2)* can serve as the descriptor to predict the catalytic performance of BACs. Most importantly, the optimal limiting potential of Mn2 BAC can reach a significant −0.26 V via an enzymatic pathway. These results compare catalytic activities between SACs and BACs and provide a theoretical basis for exploring novel, highly efficient electrocatalysts for NRR.

Two-dimensional Ti3C2 MXene is a promising electrode material for high-capacity supercapacitor, which is normally prepared by selective etching of the Al layer from ternary carbide Ti3AlC2 MAX phase using HF acid solution. Here a distinct etching method using a little HF acid is reported. Ti3C2 MXene decorated with Ag nanoparticles are synthesized via a chemical replacement reaction with AgNO3 solution at room temperature and then evaluated as working electrodes. Due to the synergistic effect between Ag and Ti3C2 matrix, the resulting composite of the 10 wt% AgNO3 treated sample (Ag-10) exhibits higher specific capacitance of 779.5 F g−1 at the scan rate of 5 mV s−1 in 6 M KOH electrolyte solution and shows good cycling stability with capacitance retaining 95% after 5000-cycles. This work also shows the possibility of using other metallic cations with higher redox potential to prepare high performance MXenes for supercapacitor materials.

With the consumption of fossil fuels, energy and environmental problems have become increasingly prominent. Finding new energy to replace traditional fossil fuels is one of the most promising approaches to solve current energy shortages and environmental problems. Fuel cells are not restricted to Carnot cycles when chemical energy is converted to electrical energy. It has the advantages of high energy conversion efficiency, cleanliness and environmental friendliness, and occupies an important position in the fields of new energy. However, slow cathode kinetics is an important reason which has limited development of fuel cells. The traditional Pt-based catalysts with poor stability, CO poisoning, high price and other shortcomings have been unable to meet the demands for serving as fuel cell catalysts. In recent years, the non-precious metal catalysts have been widely recognized for their higher stability and resistance to CO poisoning, which are cheaper than Pt-based catalysts. Scientists have made many efforts in research of non-precious metal catalysts. This review summarizes the research progress of non-precious metal catalysts in the field of fuel cells in recent years, mainly including non-metal doped carbon materials, metal and non-metal co-doped carbon materials, and the catalytic mechanism of various catalysts.