Controllable Preparation Of Nanocarbon Materials-based Electrocatalysts

As environmental issues and global energy shortages become increasingly prominent,more and more researchers are striving to find new renewable energy sources to replace fossil fuels.As an ideal clean energy and important chemical raw material,hydrogen has received widespread attention worldwide.Electrocatalytic water cracking is an important means of low-cost large-scale production of hydrogen,and it is also considered to be one of the potential strategies to solve above-mentioned two major social problems.Due to the high overpotential of hydrogen production by electrolysis of water,an effective and stable electrocatalyst is needed to accelerate the reaction kinetics of cathodic hydrogen evolution（HER）and anodic oxygen evolution（OER）reactions.Studies have shown that Ru and Ru O₂ have high catalytic activity for HER and OER under acidic,neutral,and basic conditions.However,as a precious metal,Ru still has shortcomings such as high price,low reserves,and poor stability.Introducing transition metals into Ru-based catalysts and loading them on conductive carbon materials can not only effectively reduce the amount of Ru,but also form nanoparticles that can be uniformly dispersed on conductive carbon materials and generate strong electronic interactions with the carrier,resulting in higher catalytic activity and stability of Ru-based catalysts.Based on this,three bimetal-loaded heteroatom-doped carbon materials were prepared,which showed outstanding catalytic activity and good stability for water electrolysis.The results obtained are provided as follows.1.RuCoalloy loaded S,N dual-doped carbon nanotubes,labelled as RuCo/S,N-CNTs-T（where T denotes the pyrolysis temperature）,were successfully synthesized by a simple hydrothermal vulcanization method with combination pyrolysis at different temperatures in an inert atmosphere.The optimized RuCo/S,N-CNTs-900 catalyst displayed outstanding catalytic activity for HER and OER in 1 mol/L KOH alkaline solution.The over potential of HER and OER is only 45 m V and 290 m V at a current density of10 m A cm^-2.The RuCo/S,N-CNTs-900 catalyst was loaded on foam nickel as the anode and cathode of the all water cracking unit,and the current density reached 10 m A cm^-2 at 1.57 V of the cell voltage.The as-obtained catalyst also showed excellent durability and long-term stability.2.The S and N doped carbon supported Ru O₂/CoSO₄ nanoparticles,named Ru O₂/CoSO₄-NSC-T（where T represents the calcination temperature）were prepared by a facile hydrothermal reaction with combination of low temperature calcination.The as-prepared Ru O₂/CoSO₄-NSC-400 catalyst showed excellent activity in 1 M KOH solution,with low overpotential of 70m V to reach 10 m A cm^-2 for HER and low overpotential of 225 m V to achieve 10 m A cm^-2 for OER,respectively.The water electrolyzer assembled with Ru O₂/CoSO₄-NSC-400 as the cathode electrode and anode electrode,respectively,needed a cell voltage of 1.60 V to achieve a current density of 10 m A cm^-2and displayed excellent stability and durability.3.Ru O₂ nanoparticles loaded N and Ni co-doped carbon nanotubes were prepared by high-temperature pyrolysis and subsequent acid etching with combination a secondary calcination strategy using amino-functionalized carbon nanotubes-dispersed chitosan hydrogel as the carbon and nitrogen sources,and Ru Cl₃ and Ni Cl₂ as the metal sources.The morphology,structure and crystalline phases were analyzed by scanning electron microscopy（SEM）,transmission electron microscopy（TEM）and powder X-ray diffraction（XRD）techniques.The results indicated that the chitosan was decomposed during high temperature pyrolysis and the catalyst retained the morphology of carbon nanotubes.The subsequent acid leaching removed the unstable Ni species,and the Ru O₂ nanoparticles loaded on N and Ni co-doped carbon nanotubes was produced after secondary calcination of the pyrolyzed and acid-leached hybrid material.The optimized catalyst showed excellent bifunctional performance of HER(60 m V@10 m A cm^-2)and OER(234m V@10 m A cm^-2)in 1M KOH solution.The assembly of the overall water splitting device only a tank voltage of 1.58 V to obtain a current density of10 m A cm^-2 with excellent stability.