Preparation Of Molybdenum Carbide/Nanocarbon Composites As Electrocatalysts For Hydrogen Evolution Reaction

The environmental problems brought by traditional fossil fuel energy have gradually become the central issue of community.The pursuit of clean and green energy is vital to sustainable development.Hydrogen is a renewable energy source with high energy density and no pollution,which has proven to be a potential energy source for fuel cell applications.Water splitting by electrolysis is regarded as an attractive method for large-scale hydrogen production and has become a hot spot of research.The electrolysis of water needs to overcome the high overpotential to generate a large current density,which results in slow reaction kinetics process,and the overall energy conversion efficiency is greatly reduced.Therefore,high-efficience catalysts are essential for the hydrogen evolution reaction?HER?.At present,the highest catalytic efficiency of the HER catalyst is a platinum-based precious metal catalyst,but high cost,low reserves and poor stability limits the wide application of such catalysts.Hence,it is urgent to research and explore efficient non-precious metal Catalysts.Recently,the investigation of transition metals as HER catalysts has attracted more attention.Among them,molybdenum-based composites have excellent catalytic properties for HER due to a platinum-like d-band electronic structure,which making them one of the alternative noble metal catalysts.Arc discharge is a method of preparing high-defect carbon nanomaterials,which are critical to the uniform loading of nanoparticles.In this paper,we proposed to fabricate a series of molybdenum/carbon nanocomposite catalysts by using arc discharge method and discussed their catalytic performance for HER.2.Molybdenum-basedcompound/carbonnanosheetcomposites?MoCx/CNS?were prepared by arc discharge in different concentrations of ammonium molybdate solution.XRD and TEM characterization results showed that the nanoparticles of particle size of 6.68 nm are relatively uniformly loaded on the carbon nanosheet with a high degree of crystallization from the optimal MoCx/CNS sample prepared at a concentration of 0.1 mol L^-1.In addition,molybdenum carbide/carbon nanosheet composites?MoCx/CNS-700?were prepared by carbonization at 700°C.The XRD and TEM characterization results showed that the nanoparticle form is converted into a molybdenum carbide structure and the average particle size is reduced to 2.74 nm,which makes possess excellent performance in the hydrogen evolution reaction.The corresponding overpotential at-10 mA cm^-2 current density is-221 mV and the Tafel slope is 68.1 mV dec^-1.In the stability test,the overpotential drops 4 mV after 1000 cycles of CV,and the current density decreased by 7%after i-t curve of test 10 hours,which showing superior stability.2.Molybdenum carbide/carbon nanosphere composites?Mo₂C/GNs?were prepared.High-defective GNs were prepared by using arc discharge method in toluene solution with oxygen functional groups at the edges,showing high the characteristics of the defect.Mo₂C/GNs were then prepared using GNs as a template.By controlling the loading and carbonization temperature,the optimal hydrogen evolution catalyst?Mo₂C/GNs-700?was obtained under the theoretical mass ratio of GNs to molybdenum element of 1:1 and 700°C.The XRD,SEM and TEM results showed that Mo₂C/GNs-700 was loaded with ultrafine molybdenum carbide nanoparticles at the edge of GNs with a particle size of1.87 nm.The results of HER showed that the corresponding overpotential at current density of-10 mA cm^-2 was-196 mV,the Tafel slope was 58.6 mV dec^-1,and the exchange current density was 1.1x10^-2 mA cm^-2.It has excellent catalytic performance and good stability.In this paper,a series of molybdenum/nanocarbon composites were prepared by liquid plasma arc discharge method,the effects of different nanocarbon forms on the morphology,structure and properties of the catalysts were investigated.It provides a new idea for the preparation of non-precious metal catalysts,and has guiding significance for the development of electrolyzed water in the hydrogen production technology.