Designed Synthesis Of Two-Dimensional Carbon Nitride And Molybdenum Sulfide(Selenide) For Photo/Electrocatalytic Hydrogen Evolution

The development of aeronautical and astronautical power technology is based on the continuous progress of aircraft fuel technology.Hydrogen?H2?is a new,clean and renewable energy carrier with high quantity of combustion to replace the traditional fossil fuels,which is of great significance for the upgrading of aerospace power technology.Meanwhile,on the alien planets with water resource,it is the most ideal way to establish human living environment by using light energy or electric energy transformed from light to promote water splitting and obtain clean hydrogen energy and oxygen?O₂?.Since the hydrogen can be obtained through direct water splitting?Hydrogen Evolution Reaction,HER?,it is an attractive and inevitable choice to develop and design efficient,inexpensive and earth-abundant photo-/electro-catalysts.In this study,to achieve highly efficient photo/electrocatalytic hydrogen production,two-dimensional?2D?materials with unique structure and photo/electro-catalytic properties were investigated and the facile methods to prepare 2D nanomaterials with atomic thickness were also presented.Furthere,2D nanostructures with synergistic catalytic effect were designed and synthesized to ultimately achieve efficient HER performance.Firstly,a visible,highly efficient,and controlable liquid ammonia assisted lithiation method?LAAL?was presented to intercalate amd exfoliate 2D layered graphite carbon nitride?g-C₃N₄?,and high-quality few-layer-thick two-dimensional g-C₃N₄ nanosheets?NS?were obtained.The Li intercalation reaction in this method is very rapid?less than half an hour?,and the process canbe judged by observing the color change of LA solution.The obtained g-C₃N₄ NS maintained the similar crystal structure and chemical stoichiometric ratio relative to the parent bulk materials,but the surface structure,electronic conductivity and specific surface area were significantly optimized.Moreover,compared to the bulk counterparts,the as-prepared g-C₃N₄ NS show clearly enhanced photocatalytic H2 evolution?hydrogen production rate 570 mmol/g.h?,which is two magnitude higher than that of bulk g-C₃N₄.Moreover,LAAL is a general method and could be easily extended to exfoliate diverse other 2D layered materials such as molybdenum sulfide?MoS₂?,tungsten sulfide?WS₂?and molybdenum selenide?MoSe₂?etc.MoS₂ is a promising 2D catalyst for the hydrogen evolution reaction?HER?that has been extensively studied due to its excellent performance,but the lack of understanding on the factors that impact its catalytic activity hinders further design and enhancement of MoS₂-based electrocatalysts.Here,to construct a MoS₂ catalytic system with multi-factor coordination of “phase-defect”,LAAL route was used to achieve the novel porous 1T-MoS₂ NS,and five representative MoS₂ NS samples,including 2H and 1T-phase,porous 2H and 1T-phase,and sulfur compensated porous 2H-phase were also fabricated.We systematically investigated the contributions of crystal structure?phase?,edges,and sulfur vacancies?S-vacancies?to the catalytic activity towards HER based on the five representative samples.A comparative study revealed that not only phase serves as the key role in determining the HER performance,but also both edges and S-vacancies also contribute significantly to the catalytic activity in porous MoS₂ samples,as shown by detailed defect characterizations.Ultimately,superior synergistic catalytic activity was achieved in the porous 1T-phase MoS₂ NS with an overpotential of 153 m V vs RHE for the electrocatalytic current density of j =-10 m A/cm2,and a Tafel slope of 43 m V/dec,which is among the best MoS₂-based catalysts.MoSe₂ is another important electrocatalyst for hydrogen evolution reaction?HER?.In this study,to realize synergistic catalysis of “phase-disorder” in MoSe₂ system,we present a novel hydrothermal synthesis strategy to achieve simultaneous and synergistic modulation of crystal phase and disorder in partially-crystallized 1T-MoSe₂ NS.Specifically,the formation of 1T phase under large excess of the reductant during synthesis could effectively improve the electronic conductivity,and disordered structure from lower reaction temperature can provide abundant unsaturated selenium atoms as active sites,as revealed by careful defect characterazation.Such synergistic effects of 1T-phase and disorder led to superior HER catalytic activity with an overpotential of 152 m V vs RHE for the electrocatalytic current density of j =-10 m A/cm2,and a Tafel slope of 52 m V/dec,which is the best HER performance in MoSe₂-based electrocatalysts.