Applications Of MoS₂ In Nickel-metal Hydrid Battery And Hydrogen Evolution Reaction

MoS₂,layered transition metal dichalcogenide,has attracted extensive interest due to its unique properties and promising applications.Due to the weak van der Waals?vdW?interaction between layers,layered MoS₂ crystals can be exfoliated to single or few layers nanosheets,showing unusual physical and electronic properties which are different from their bulk materials.Up to now,extensive efforts have been made to prepare ultrathin MoS₂nanosheets.In order to exploit their potential and widen their applications,enormous efforts have been made in the preparation of MoS₂ nanosheets with novel structures.Due to their unique physical and chemical properties originating from their various chemical compositions,tuneable bandgaps and unique electronic structures,these ultrathin MoS₂nanosheets have been proven to be fascinating candidate materials for many applications in electronics,optoelectronics,thermoelectrics,catalysis,energy conversion and storage,biomedicine and so on.MoS₂ nanosheets are used for hydrogen storage alloys and hydrogen evolution reaction?HER?,which are mainly because of that hydrogen has been recognized as the most promising clean-energy carrier with highest energy density and environmental compatibility.Thus,the development of hydrogen economy is critical for energy crisis and environmental pollution.The hydrogen economy includes hydrogen storage and evolution.Although MoS₂ has the potential for hydrogen storage and evolution,the corresponding performances need to be further improved.Herein,MoS₂ is used to enhance the HRD performance of hydrogen storage alloys.Moreover,the catalytic performance of MoS₂ for HER is increased through the dual-modification between non-noble-metal and RGO.The details are as follows:?1?The poor high-rate dischargeability of hydrogen storage alloys has hindered applications of nickel metal hydride batteries in high-power fields,new-energy vehicles,power tools,military devices,etc.A new strategy is developed to improve the high-rate performance of hydrogen storage alloys by coating MoS₂ nanosheets on alloy surfaces.The capacity retention rate of the composite electrode reaches 50.5%at a discharge current density of 3000 mA g^-1,which is 2.7 times that of bare alloy?18.4%?.The density functional theory?DFT?simulations indicate that such an outstanding performance is derived from adjustments of ion concentrations at the electrode/electrolyte interface by MoS₂ nanosheets:?a?the higher OH^-concentration facilitates the electrochemical reaction of MH_ads+OH^--e^-?M+H₂O;and?b?the lower H⁺concentration leads to a large gradient between the electrode/electrolyte interface and interior of alloys,which is beneficial for the diffusion of atomic hydrogen during the discharging process.?2?MoS₂ has attracted ever-growing interest as one of the most promising non-noble-metal electrocatalysts for HER.However,its catalytic efficiency is far from that of Pt-based catalysts due to insufficient active sites and poor conductivity.Our DFT simulations indicate that the catalytic activity of MoS₂ could be improved through synergistic effects between the graphene substrate and Ni atom adsorption.Following this result,we designed and synthesized dual-modified MoS₂ nanosheets with nanoporous Ni and RGO,which show a low onset potential?85 mV?,a small Tafel slope(71.3 mV dec^-1),and a high cycling stability as HER catalysts.Both the DFT and experimental results demonstrate that the above superior performances are derived from a large number of edge active sites and fast electron transport.This study provides a comprehensive understanding of the HER activity of MoS₂.?3?Electrochemical water splitting driven by renewable electricity is a promising pathway for sustainable hydrogen production,where the catalysts with high efficiency and economic benefit are urgently needed.MoS₂ is considered a promising electrocatalyst for HER to replace highly efficient,but expensive Pt-based catalysts.Our DFT calculations reveal that the catalytic performance of MoS₂ is dramatically improved through alloying with cobalt atoms and compositing with graphene.Furthermore,we successfully synthesize?CoMo?S₂/RGO as an excellent electrocatalyst for HER.The corresponding onset potential is 28 mV and the overpotential is 100 mV when the current density reaches 10 mA cm^-2,which have obvious advantages compared to other MoS₂-based catalysts.Both the DFT calculations and experimental results demonstrate that the outstanding catalytic performance is derived from abundant active sites and high intrinsic activity of each active site through the synergistic effects between cobalt atoms and RGO.