Preparation Of Nanoporous Two-dimensional Metal Compounds And Electrocatalytic Ammonia Synthesis

Due to their unique physical structure and chemical properties,twodimensional metal compounds have attracted widespread attention in scientific research and industrial circles,and have shown great applications in frontier fields such as elec tronic/op to electronic devices,catalysis,biomedicine,and energy storage systems.However,sheet-like twodimensional metal compounds are prone to aggregation and stacking,which strongly limits their properties and applications.On the basis of retaining the physical and chemical properties of metal compounds,rationally constructing two-dimensional materials with three-dimensional structures(3D)is an effective method to solve this problem.Moreover,no large-scale synthetic method exists at present that delivers all of the small size,controllability(including pore size and thickness),and repeatability,which seriously limits the expansion and large-scale application of their systems.Therefore,it is an urgent need to exploit a method for the large-scale preparation of two-dimensional metal compounds with three-dimensional structures.In view of the above key problems,with the help of phase diagram theory,recyclable nano porous gold(NPG)was used as template catalyst.Based on surface alloy strategy,nano porous two-dimensional metal compounds and their composites are successfully prepared by nanoporous gold-assisted chemical vapor deposition.The formation mechanism of surface alloy in the growth process was systematically clarified by combining experiment and theory.Furthermore,it was applied to the electrocatalytic nitrogen reduction to ammonia synthesis reaction,and the catalytic kinetic process and mechanism of electrocatalytic nitrogen reduction to ammonia were revealed.The main research contents and results are as follows:1.With the help of the metal phase diagram theory,we have demonstrated a general nanoporous gold-assisted chemical vapour deposition method for the production of nanoporous two-dimensional metal compounds.The transition metal(M)atoms were first diffused onto the nanoporous gold(Au)surface to form the Au-M surface solid solution alloy,and then the surface alloy was exposed to the corresponding precursor vapor(X)to form the MXn@NPG material,finally the synthesized materials were selectively etched with KI/I2.19 binary compounds and 5 alloyed compounds were successfully prepared through the free choice of Au-M,including nitrides,carbides,sulfides,selenides,and tellurides.The atomic growth regulation of the as-grown nanoporous metal compounds are further revealed by High resolution electron microscopy.In addition,the lattice strains introduced by the 3D bicontinous curvature of samples to make lattice stretching,which can effectively regulate the phase transition of 2D metal compounds.and realize the coexistence of metal(1T)and semiconductor phase(2H).Benefiting from nanoporous bicontinuous structure and abundant adsorption active sites,the resulting 3D nanoporous MoSSe exhibits excellent electrochemical N2 reduction reaction properties.2.A vacancy-rich nanoporous MoSe2 supported single Au atoms(denoted as AuSA/np-MoSe2)was successfully fabricated by the combination of chemical vapor deposition process and chemical etching.The catalyst exhibits excellent nitrogen reduction performance with a high NH3 yield of 30.83 μg h-1 mg-1 and a Faradaic efficiency of 37.82%at a relatively low potential(-0.3 V vs.RHE),with the performance of 8.9 times higher than that of np-MoSe2,while also outperforming most of the reported electrochemical nitrogen reduction catalysts.The theoretical analysis results show that the introduction of Au single atoms on the np-MoSe2 substrate is beneficial to the adsorption and diffusion of N2,and also reduces the dissociation energy barrier of N2.Morever,the introduction of Au moves MoSe2 away from the optimal potential for hydrogen evolution,suppressing the competing reactions of hydrogen evolution,thus enhancing the catalytic selectivity towards N2 electroreduction.3.We have demonstrated a general approach to realize scalable nanoporous transition metal doped ReSe2 via surface co-alloy strategy.The TM and Re atoms were first diffused onto the nanoporous gold(Au)surface to form TM-Re-Au surface co-alloy,followed by selenization of the surface co-alloy to TM-ReSe2@NPG,and finally the NP TM-ReSe2 were obtained by selectively removing the nanoporous gold substrate in a KI/I2 aqueous solution.Theoretical calculations show that the formation of TM-rich regions on the Au(111)surface is good for the movement of Re atoms in the alloy and the subsequent adsorption,nucleation and growth of TM-ReSe2.The strain induced by structural curvature and atomic doping effect to make Re atoms lattice stretching,we successfully obtained high purity(87%)twisted phase ReSe2.It is worth noting that the NP Ru-ReSe2 catalyst exhibits excellent nitrogen reduction performance.The ammonia yield is 19.41 μgh-1 mg-1,the Faraday efficiency is 22.69%at-0.4 V vs.RHE.The theoretical results show that the introduction of Ru atoms onto NP ReSe2 can regulate the formation of surface selenium vacancies to serve as the active sites of NRR,which effectively promote the adsorption and activation of N2 molecules.The NRR reactions follow the distal hydrogenation pathway.In summary,binary and ternary nanoporous two-dimensional metal compounds,nanoporous MoSe2 loaded Au monatoms and transition metal doped nano porous ReSe2 were constructed on the atomic scale by nanoporous gold-assisted chemical vapor deposition.They were applied in the field of electrocatalytic N2 reduction.This paper not only solves the technical problem of large-scale preparation of nanoporous two-dimensional metal compounds,but also provides new ideas and approaches for further designing and regulating the performance of electrocatalytic N2 reduction to ammonia.