Controllable Synthesis And Electrocatalytic Water Splitting Performance Of Ruthenium-Modified Transition Metal Hydroxides

On account of the rapid development of industrialization and the over-exploitation of fossil energy,that has led to increasingly severe energy crisis and environmental pollution problems.As an ideal clean energy and raw material for chemical production,hydrogen has received extensive attention from countries around the world.Electrocatalytic water splitting is an important way for large-scale and low-cost hydrogen production,and it is also considered as one of the potential strategies to solve these two major social problems.Rational design of cost-effective and stable catalysts is a major problem in current electrocatalytic hydrogen evolution reaction（HER）.Platinum-based（Pt）catalysts are considered the best hydrogen evolution catalyst,but the low natural content and high price of platinum limit the large-scale production.Designing and developing high-performance and low-cost catalysts supported by decreasing noble metals has become one of the solutions to this problem.In this paper,Ru（ΔG_H is close to Pt）with only 1/3 of the price of Pt is introduced into the transition metal-related catalyst system.After a lower content of Ru（Ru doped,Ru nanoparticles）is introduced into the system,it can interact with the substrate and effectively regulate the electronic structure of the system and improve the HER performance of the sample.The details are as follows:1.A green,facile,and time-saving synergetic strategy of Ru doping and air plasma was adopted to effectively improve the HER performance of Co Ni-LDH nanosheets assembled nanotube arrays（NTAs）that is in situ transformed from ZIF-67 nanorod arrays.Ru doping and air plasma treatment not only tune the oxygen vacancies of Co NiLDH to optimize the electronic structure,but also increase the surface roughness and hydrophilicity,thus greatly enhancing its catalytic activity.The Ru-doped Co Ni-LDH nanotube arrays after air plasma treatment（P-Ru-Co Ni-LDH）exhibit excellent HER performance,requiring only 29 m V overpotential to achieve a current density at 10 m A cm^-2.Furthermore,only a lower cell voltage of 1.36 V is required at 10 m A cm^-2 when P-Ru-Co Ni-LDH acts as both the cathode and anode of the urea oxidation-assisted water splitting.And after 100 h of continuous i-t test,the activity of the sample did not decrease significantly,showing excellent stability.Therefore,the HER performance of P-Ru-Co Ni-LDH was optimized through electronic structure modulation and surface wettability improvement,and the designed synergistic strategy can be applied to develop other types of catalysts.2.By combining defect anchoring and in situ reduction,a layer of Ru nanoparticles was uniformly deposited on the surface of D-Co Ni-LDH containing cation vacancies at room temperature.First,Al-doped Co Ni-LDH was synthesized by in situ transformation of ZIF-67,and D-Co Ni-LDH with metal cation vacancies was formed by alkali etching.Due to the electrostatic adsorption between cation vacancies and Ru³⁺,Ru can be uniformly dispersed on the surface of the sample and generate anchoring Ru nanoparticles.The as-prepared uniform Ru-D-Co Ni-LDH catalyst requires only an overpotential of 21 m V to reach a current density of 10 m A cm^-2.The Ru nanoparticles in the samples can effectively tune the electronic structure of Co NiLDH,optimize the Volmer step of HER,and the adsorption and desorption of atomic H,thus significantly enhance HER performance.Moreover,the OER stability of the DCo Ni-LDH sample after the introduction of cationic vacancies has been greatly improved compared with the Co Ni-LDH sample,which provides a high performance and high stability for the design and development of other related catalytic fields.3.With the aid of melamine,we derivatized Ni Fe-LDH into Ni₃ Fe nanoparticlesterminated nitrogen-doped carbon nanotubes（N-CNTs）by a one-step high-temperature catalytic method,which showed better OER performance than Ni Fe-LDH.The outlayer N-CNT provide a stable chain mail for the inner Ni₃ Fe nanoparticles,thus,the OER stability of the sample has been greatly improved.Compared with Ni Fe-LDH,its current decays by only 8% after cycling at a current density of 100 m A cm^-2 for 100 h.In addition,through the reducibility of Ni₃ Fe alloy and the anchoring effect of N defects in carbon nanotubes,a layer of uniformly distributed fine Ru nanoparticles is formed on the surface of carbon nanotubes by in-situ reduction,which greatly improves the HER performance of the sample.The sample only needs an overpotential of 25 m V to achieve a current density of 10 m A cm^-2 and has a low Tafel slope of 28.1 m V dec^-1.The 100 h stability（i-t）test was performed at 50 m A cm^-2,and the current of the sample did not change significantly.The structure of this nitrogen-doped carbon nanotubecoated Ni₃ Fe alloy that we have constructed not only puts on chain mail for the catalyst,but also provides a powerful tool for catalysis after the surface is loaded with Ru nanoparticles.The high activity and stability and low noble metal loading of the overall water splitting catalyst have the potential for practical application.