Preparation Of Self-supported Nanocatalysts And Application In Electrochemical Water Splitting

Developing efficient electrocatalytic materials plays a key role in electrochemical water splitting systems.Many strategies have been proposed to increase the number of exposed active sites and to enhance the intrinsic activity of each active site.Nanomaterials process high surface area,which provide abundant active site.Significant research efforts have thus been devoted to the development of electrochemically active nanomaterials.Compared with those nanomaterials in a powdery from,self-supported nanomaterials exhibit many advantages,including higher surface area,better electrochemical stability,and facile preparation methods.Benefiting from these merits,self-supported nanomaterials are deemed as promising catalysts for electrocatalytic water splitting system.The purport of this dissertation is to develop new synthetic methods for the preparation of novel self-supported nanomaterials.Besides,it is also expected to obtain superior water splitting activity by modulating the composition and structure of self-supported catalysts.The main contents include:?1?Detailed characterizations were performed to investigate the structure of catalyst after electrocatalysis.It is found that cobalt disulfide is not stable under oxidative potential during the electrocatalysis.Such instability is utilized for the conversation from cobalt disulfide nanowire array to cobalt borate?Co-B_i?nanowire array.Based on this result,we broadened the application of electrochemical conversion.Benefiting from the nanoarray structure,the as-prepared Co-B_i nanowire array exhibits a much better oxygen evolution activity than previously reported Co-B_i film.In 0.1 M potassium borate?pH=9.2?,Co-B_i is able to derive 10 mA cm^-2 at a low overpotential of 411 mV.?2?By optimized electrochemical conversion method,nickel selenide nanosheet array was converted to nickel borate nanoarray?Ni-B_i?.The three-dimensional structure of Ni-B_i nanoarray enables a more efficient diffusion of electrolyte and thus significantly enlarged electrochemical surface area.In 0.1 M potassium borate,Ni-B_i nanoarray shows a low overpotential of 430 mV at a current density of 10 mA cm^-2.Moreover,Ni-B_i nanoarray also shows good stability and high turnover frequency.?3?Using electrochemical conversion method,NiCo₂O₄ nanowire array was converted to core-shell structured NiCo₂O₄@Ni-Co-carbonate nanoarray?NiCo₂O₄@Ni-Co-C_i?.In 1.0 M potassium bicarbonate?K-C_i,pH=8.4?,NiCo₂O₄@Ni-Co-C_i nanoarray shows a low overpotential of 309 mV at a current density of 10 mA cm^-2.Such good activity is the best under mild conditions.The high performance comes from the abundant active sites and high intrinsic activity of amorphous Ni-Co-C_i layer.Compared with borate-based catalysts,such NiCo₂O₄@Ni-Co-C_i has the merits of better environmental compatibility and wider availability.?4?We develop a benzoate anion-intercalated layered cobalt hydroxide nanobelt array on nickel foam?benzoate-Co?OH?₂/NF?through a one-pot hydrothermal process.In 1.0 M KOH,the as-prepared benzoate-Co?OH?₂/NF drives a high catalytic current density of 50 mAcm^-2 at an overpotential of 291 mV,outperforming most of the cobalt-based materials.By combining the advantages of expanded interlayer spacing and nanoarray structure,benzoate-Co?OH?₂/NF exhibits high activity toward the oxygen evolution reaction.The intercalation of a benzoate anion expanded the interlayer spacing,leading to more exposed active sites.?5?We reported self-supported RuP and RuP₂ catalyst films on carbon cloth?RuP/CC and RuP₂/CC?,which are prepared by a dip-coating method and a subsequent phase-controllable phosphorization treatment.RuP/CC displays superior hydrogen evolution activity with a low overpotential of 13 mV at 10 mA cm^-2.Such high activity is one of the best among the reported values.Density functional theory calculations reveal that Ru site is the active site for hydrogen adsorption.RuP with a higher charge density at the Ru site is more favorable for the chemisorption of hydrogen,thereby exhibiting better hydrogen evolution activity than RuP₂.We provided not only an efficient catalyst for hydrogen evolution,but also an insight into the phase-activity relationship of phosphide.