Study On Modification Of Potassium Niobate And Its Performance On Electrochemical Nitrogen Reduction Reaction

Ammonia（NH₃）,one of the important chemical raw materials,is a carbon-free energy carrier with great potential in the future energy economy.At present,industrial ammonia is mainly produced by Haber-Bosch process,which has a series of negative effects on the ecosystem and greenhouse gas balance.Electrochemical nitrogen reduction reaction（NRR）for NH₃ production is one of the most promising alternatives to the energy-intensive Haber-Bosch process,owing to its clean,efficient,sustainable,and eco-friendly advantages.However,with the lack of effective electrocatalysts,the research for NH₃ yield（r）and Faraday efficiency（FE）are still far from the theoretical target,which is the main challenge of electrochemical NRR.As a d-block transition metal（d-TM）element,niobium（Nb）and derived compounds have great potential for NRR application.At present,few Nb-based NRR catalysts have been reported,and simultaneously the modification strategy adopted is relatively simple.Therefore,in-depth researches are required to design the efficient and stable Nb-based NRR catalysts.Potassium niobate（KNb₃O₈）has different morphologies such as block shape and rod shape,and is easy to be modified.It has been used in photocatalysis and other fields,but has not been applied to NRR.In this paper,KNb₃O₈,modified by the anionic doping,partial hydrogenation,morphology control and other modification strategies to improve the apparent activity or intrinsic activity,were applied to investigate the performance of NRR.The specific content was divided into the following three parts:（1）P-doped bulk KNb₃O₈（P-KNO）was synthesized by two steps of solid-state reaction and gas-solid reaction.NRR test showed that the best FE and r of P-KNO were 39.77%and23.01μg·h^-1·mg^-1_cat,respectively,with the ideal stability and selectivity.In the phosphating process,P was successfully incorporated and additional oxygen vacancies were generated in the KNb₃O₈,which effectively improved the intrinsic activity of the active site.（2）Partially hydrogenated bulk KNb₃O₈（b-H-KNO）nanomaterials with layered structure were prepared by a simple two-step synthesis method,and their structural composition was further characterized.The r and FE in 0.1 M Na₂SO₄ reached 17.86μg·h^-1·mg^-1_cat and 60.57%,respectively,and the performance remained stable after five cycles.Through a series of comparative tests,it was found that the excellent performance was mainly attributed to the improvement of electronic environment by H inserted into the lattice by partial hydrogenation.The experimental results indicates that b-H-KNO with layered structure has great potential to be used as NRR catalyst,which provides an idea for the design of efficient and stable 2D NRR electrocatalyst.（3）The rod KNb₃O₈（r-KNO）was prepared by changing the K source and calcination conditions,and the nanorod r-H-KNO with layered structure was also obtained by partial hydrogenation.Through electrochemical analysis,the NRR performance in 0.1 M Na₂SO₄ was better than that of bulk material（b-H-KNO）at lower overpotential——the best NH₃ yield reached 21.47μg·h^-1·mg^-1_cat,and the FE was 63.17%.The improvement of its electrocatalytic performance was mainly due to the enhanced exposure of active sites in the nanorod,which enhanced the apparent activity.Thus,it is favorable for the adsorption of N₂.In addition,it was found to have good electrochemical and structural stability after 5 cycles of testing.The results show that the modified KNb₃O₈ exhibits high catalytic activity and stability for NRR.The modification strategies,including anion doping,partial hydrogenation and morphology control,can improve the performance of NRR catalyst,which provide ways for rational design and preparation of efficient NRR catalysts.