The Effect Of Modification On VS₂ Based Materials For Electrocatalytic Nitrogen Reduction Reaction

Electrocatalytic nitrogen reduction reaction（NRR）can effectively improve conventional Haber-Bosch technology with energy-extensive depletion and massive carbon dioxide（CO₂）emissions due to its mild reaction requirements（normal temperature and pressure）.The main problems for NRR are as follows:（1）low solubility for nitrogen（N₂）;（2）high bond energy for N≡N and（3）the severe competitive hydrogen evolution reaction（HER）.Based on the above problems,reasonable development of electrocatalysts with excellent performance is an important key for NRR.VS₂ material has the superior electronic structure for transition metal sulfides,which is worthy of further studying due to its high ammonia yield as NRR electrocatalyst.In this work,different strategies were adopted to regulate the physicochemical properties of VS₂ based materials centered on the modification design of efficient NRR electrocatalysts.The reasons for the improvement of catalytic performance on NRR were explored from the aspects of electronic structure and interfacial microenvironment,and the reduction reaction process and action mechanism were explicated.Our works are as follows:（1）Boron（B）doped VS₂（B-VS₂）and pure VS₂ catalysts were synthesized by simple hydrothermal method.At?0.3 V vs.RHE,B-VS₂ had the ammonia yield of 58.0μg h^?1 mg_cat^?1 with the FE of 11.4%;after five cycles,the average values become 53.0μg h^?1 mg_cat^?1 and 10.8%,respectively,which were much better than that of the undoped VS₂.In situ experiments showed that the V⁴⁺active sites in B-VS₂ were well stabilized during the reaction,which effectively improved the activity and selectivity for NRR.On the contrary,the V⁴⁺in VS₂ was reduced under applied potentials,leading to a decrease in the reaction performance.Theoretical calculation results showed that the B–S–V bond formed in B-VS₂ after B doping promoted the interatomic electron transfer and inhibited the reduction from V⁴⁺to V²⁺at low overpotentials,thus achieving the purpose of stabilizing the active site and improving the reaction performance.（2）The surface alkyl thiol modified VS₂（C_x-VS₂）and pure VS₂ catalysts were prepared by hydrothermal method and soaking method.Alkyl thiols were selected as 1-Butanethiol（C₄）,1-Octanethiol（C₈）and 1-Dodecanethiol(C₁₂).Compared with unmodified VS₂ catalyst,C_x-VS₂ showed higher NRR activity and selectivity due to its strong hydrophobicity and N₂ affinity.Among them,C₈-VS₂ catalyst had the best catalytic performance with the ammonia yield of58.4μg h^?1 mg_cat^?1 and the FE of 34.7%at?0.2 V vs.RHE.The gas/liquid contact angle tests,in situ tests and theoretical calculations demonstrated that the unique interface microenvironment caused by alkyl thiol resulted in the optimal hydrophobicity and N₂ enrichment for C₈-VS₂catalyst with little effect on active sites.In summary,C₈-VS₂ catalyst had the best NRR performance compared to others.In a word,the effect and mechanism of modification strategies for VS₂based catalysts on improving the performance of electrocatalytic NRR were deeply discussed by preparing B-VS₂ and C₈-VS₂ catalysts.Firstly,the experiments and theoretical calculations were carried out to define the ability of B doping strategy to stabilize V⁴⁺active sites in VS₂,revealing the connection between the internal electron and catalytic properties.For the problem of poor selectivity of VS₂ found in the above experiment,alkyl thiols with hydrophobicity and N₂ affinity properties were used for surface modification.The effective design on interface microenvironment can improve the electrocatalytic activity and selectivity of VS₂ based catalysts,revealing the relationship between the rational regulation of catalytic interface microenvironment and NRR performance.The above research provides feasible guidance methods for boosting the development of VS₂ based and transition metal materials.