钼基碳掺杂二硫化钼电极的硫氧化反应性能

Performance of molybdenum-based carbon doped molybdenum disulfide electrode for sulfur oxidation reaction

硫钝化是阻碍硫化物氧化反应(sulfur oxidation reaction,SOR)在硫锂电池、电化学脱硫、含硫污染物资源化等领域高效进行的重要因素.二硫化钼(MoS2)因其优异的抗硫性和可调的二维层状结构而具有良好的SOR潜能,但其本征半导体性质限制了电子传递过程.本文报道了一种抗硫性钼基碳掺杂二硫化钼电极(Mo/C-MoS2),通过碳掺杂使MoS2电极具有接近热中性的硫吸附吉布斯自由能和快速转换多硫化物的能力,有效避免了硫钝化.实验结果显示,Mo/C-MoS2能以0.37 V驱动SOR反应达到10 mA/cm2,低于Mo/MoS2电极(0.41 V)和Pt电极(0.68 V),并在恒电位电解测试中保持16.5 h的抗硫钝化稳定性.透射电子显微镜(transmission electron microscope,TEM)、X射线衍射(X-ray diffraction,XRD)、X射线光电子能谱(X-ray photoelectron spectroscopy,XPS)、拉曼散射光谱表征证实,CMoS2具有1T导电相晶体结构,提升了催化反应速率.密度泛函理论(density functional theory,DFT)计算进一步阐明,碳掺杂增强了MoS2与Na2S之间的相互作用,促使元素硫向可溶性多硫化物转换,为Mo/C-MoS2电极高效SOR和稳定抗硫性的实验结论提供了理论支撑.

The traditional energy and manufacturing sectors require handling of effluent gases and liquids that involve bivalent sulfur,specifically in the forms of alkaline sulfur and hydrogen sulfur.It must be converted to a high-net-worth product of zero valent sulfur through oxidation.Anodic electro-oxidation is a green and clean method with a complete paired electrolysis system for cathode reduction of hydrogen evolution.Molybdenum disulfide(MoS2),a two-dimensional transition metal dichalcogenide(TMD),demonstrates the ability to replace exorbitant platinum-based catalysts in the hydrogen evolution reaction(HER)in amphiphilic acid-base reactions.At the same time,extensive experimental and theoretical work has demonstrated that MoS2 is capable of anchoring polysulphides and thus accelerating the redox kinetics of the sulphur oxidation reaction(SOR)through increased polysulphide conversion.This provides a new idea for designing a type of anode electrocatalytic sulphur oxidation electrode to match the reducing half reaction.However,the passivation of the electrode surface by the deposition of low-conductive sulphur during the SOR process seriously hampered its potential use.The desired catalytic materials should have a fast electron mobility,a low free energy of adsorption of sulphur and a high selectivity over sulphides,which is a challenge for the MoS2 material.A monolithic molybdenum-based carbon-doped electrode was prepared by hydrothermal synthesis of thiourea(CH_(4)N2S),L-cysteine(C3H7NO2S),and ammonia water(NH3·H2O).This electrode can effectively reduce the free energy of sulfur adsorption on molybdenum disulphide and achieve a phase transition allowing faster electron transport.On the basis of the above,it is our opinion that a proper regulation of the catalyst-sulphide interaction may promote the dissolving of the product sulphur on the electrode surface into the electrolyte and its conversion into longer-chain polysulphides(Sx 2–),thus effectively preventing the occurrence of passivation.Catalyst characterisation,such as transmission electron microscopy(TEM),X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS),and Raman spectrum,has demonstrated that C-MoS2 has a 1T conducting phase crystal structure,which enhances the catalytic reaction rate.The experimental results show that molybdenum foil-based carbon-doped molybdenum disulfide(Mo/C-MoS2)can drive the SOR reaction up to 10 mA/cm2 at 0.37 V,which is lower than that of Mo/MoS2(0.41 V)and Pt electrode(0.68 V),and maintain the stability against sulfur passivation for 16.5 h in the constant potential electrolysis test.DFT calculations show that carbon doping enhances the hybridisation effect of molybdenum disulphide with sulphides,promotes the adsorption of polysulphide intermediates on the catalyst surface and reduces the reaction energy barrier for polysulphide conversion.The D-band centre(εd)of C-MoS2 and MoS2 and the phonon density of state(PDOS)of their stable adsorption configurations are calculated to investigate the intrinsic reason for the strong adsorption of sodium sulfide on C-MoS2.1T C-MoS2,with superior electron transfer capability over 2H MoS2,also offers new catalytic adsorption sites for intermediate sulphur(S),resulting in a thermally neutral sulphur adsorption free energy.In our opinion,the use of the Mo/C-MoS2 material as sulphur-producing electrocatalytic electrode with high stability and resistance to sulphur passivation could solve the phenomenon of sulphur passivation on the electrode surface and achieve the continuous SOR reaction.This paper broadens the application of molybdenum disulphide and provides a new solution to electrode passivation in the actual SOR process.