Assembling MXene To Mesoscale Three-Dimensional Architecture For Electrocatalytic Water Splitting

Hydrogen energy is the ultimate energy in the future.Efficient utilization of hydrogen energy is the key to getting rid of the dependence on fossil energy and sustainable development for mankind.Electrochemical water splitting is regarded as the most environmentally friendly way for hydrogen production with the highest purity.Hydrogen production by water electrolysis is mostly carried out in acid and alkali electrolyte,which put heavy strain on freshwater resources while causing a series of problems like environmental pollution and equipment corrosion for practical use.There is 13.7 trillion m3 seawater in our planet,its pH is close to neutral(8.0-8.5),and contains rich energy reserves than fossil fuels,making it a huge source for hydrogen energy resources.China's ocean area is about 3 million square kilometers.Therefore,the development of hydrogen production technology applicable to the complex ionic environment such as full pH range and seawater is of great strategic significance to both the development and utilization of marine resources and the guarantee of national energy security in China.As a rapidly rising star in 2D nanomaterial,MXene has shown great promise in the field of catalysis by excellent surface chemical activity and hydrophilicity.However,strong tendency to irreversible intersheet aggregation during preparation and application represents a major problem limiting its performance.In order to solve properties of MXene aerosol to obtain aggregation-resistant 3D MXene on the premise of ensuring the intrinsic properties of MXene.A general synthesis technology platform of aggregation-resistant 3D MXene based electrochemical functional materials was established by in-the above problems,the ultrasonic field was used to control the assemble behavior and pore interface situ loading,ion exchange,interface reconstruction and other chemical processes.The catalysts have shown good overall water splitting performance and excellent HER performance in full pH range and seawater.Firstly,the spatial and time scale and pore and interface structure properties of MXene are finely controlled by the ultrasonic external field.The aggregation-resistant 3D MXene powder has excellent compressive properties and redispersion ability,which reveals that 3D MXene powder has excellent 3D mechanical properties.The effect of steric hindrance on the aggregation-resistant behavior of MXene is discussed.Subsequently,3D MXene with different properties and new nanostructures was successfully created by in-situ loading,ion exchange,and interface reconstruction.A general synthesis technology platform of electrochemically functional materials with high intrinsic activity and excellent aggregation-resistant performance with controllable composition and structure was established.A new method was developed to construct alkaline-efficient electrocatalysts with highelectrochemical active surface area and fast mass and charge transfer capacity by in-situ assembling CoP on 3D MXene for water splitting.The chemical coupling and electronic synergistic effect can induce the uniform and stable dispersion of active sites.The open threedimensional structure provides an efficient active phase interface for catalytic reaction,which improves the intrinsic catalytic activity and mass charge transfer ability of the catalyst.The intrinsic response conversion mechanism of catalytic active sites during catalytic reaction was explored.The full water splitting performance of the catalyst is better than that of the noble metal combination.The catalyst exhibits high activity towards full water splitting superior to precious metals(Pt/C RuO2),low cell voltage(1.565 V),and good durability(150 h,100 mA cm-2)for driving overall water splitting in KOH solution.It can realize the efficient conversion of solar energy directly to hydrogen energy when combined with photovoltaic system.A novel hydrogen evolution catalyst in full pH range and seawater with low cost and high performance was proposed by coupling mh-3D MXene and ultra-fine platinum nanocrystals.The size reduction of Pt nanocrystals can greatly reduce the cost and improve the surface activity of Pt with high Pt utilization.The structure-activity relationship of the electronic and structural synergy between platinum and different supports was explored.The coupling effects on the electronic and band structure of platinum and the adsorption and conversion kinetics of reactive intermediates were revealed at the molecular and atomic level.The resultant catalyst fully exceeds the commercial Pt/C by 10-20 folds in mass activity for HER in full pH range with 13%Pt usage of Pt/C.It can work stably for more than 450 h at a current density of 10 mA cm-2 and even 250 h in seawater.It also shows excellent HER performance in seawater superior to commercial 20%Pt/C and reported electrocatalysts so far.This strategy offers an effective interface-engineering strategy to regulate the electrocatalysis over full pH range and seawater.