Design Of Carbon-based Transition Metal Phosphide And Carbide Composite Materials And Their Researches Of Electrocatalytic Activities

In the change of the times,mankind has been running towards a high degree of civilization,while the acquisition of natural resources is gradually increasing.Traditional fossil energy occupies a pivotal position and the impact of environmental pollution can’t be eliminated,and meanwhile people in line with the principle of survival of life has turned their attention to renewable clean energy systems and finally this idea has been identified as a new development goal.Hydrogen,as a renewable energy carrier,has an ultra-high calorific value,doesn’t harm to environment after combustion and can be recycled.And as we know,water splitting via electrocatalysis is one of the most capable hydrogen-producing strategies because the hydrogen obtained by this technology is high purity,no pollution to the atmosphere and simple operation process.Therefore,the design and synthesis of catalysts with special structures that can specifically catalyze electrolytic water to generate hydrogen and maintain long-term stability is the best way to advance clean energy storage and conversion.Taking into account the production cost,this paper prepared the cation-tunable flower-like(Ni_xFe_1-x)₂P@GCs as a HER and OER bifunctional catalyst and hexagonal Mo₂C loading Pt nano-cluster as HER catalyst,at the same time,we also characterized their phase composition and structure.Finally,we evaluated the ability of all materials to catalyze electrolytic water reaction by electrochemical performance measurements.It is well known that noble metal catalysts cannot be used on a large scale due to their low crustal abundance.Although the research based on transition metal phosphides has been emerging,the synthesis of phosphides with controllable morphology,adjustable composition and solid elaborate structure is a rather difficult subject.Herein,we report a series of flower-like electrocatalysts with cation-tunable(Ni_xFe_1-x)₂P nanoparticles encapsulated by porous graphitized carbon films（GCs）via the combination of morphology control and component adjustment.By progressively tailoring atomic ratios of Ni/Fe,electronic structure and electrocatalytic activities of(Ni_xFe_1-x)₂P can be intriguingly modified to achieve a versatile catalytic behavior for both HER and OER.DFT calculations also validate that the(Ni_xFe_1-x)₂P with optimal atomic ratio of Ni/Fe can support the|ΔG_H*|to be close optimum and decrease the adsorption energy for water,which can boost the water splitting.Meanwhile,anchoring the adjustable(Ni_xFe_1-x)₂P nanoparticles into GCs interlayers can endow these composites with more available active sites,excellent conductivity and enhanced stability.In fact,combined synergistic effect of cation-tuned(Ni_xFe_1-x)₂P nanoparticles and porous conductive GCs is the reason that these composites exhibit enhanced electrocatalytic activities,as illustrated by a low overpotential of 198 m V at j=10 m A cm^-2(255 m V at j=50 m A cm^-2)for OER.Meanwhile,the bifunctional(Ni_0.75Fe_0.25)₂P@GCs,as both cathode and anode of an electrolyser,effectuates an ultra-small cell potential of 1.541 V at j=10 m A cm^-2(1.573 V at j=20 m A cm^-2)for30 h during electrolysis of water,rivaling with commercial Ir O₂ and Pt/C catalysts.More importantly,this work can provide a thread to fabricate cost-saving,component-tunable and high-efficiency bimetallic electrocatalysts for water splitting.The cornstalk is used as a green carbon source,and then the positive hexagonal Mo₂C nanodisks are synthesized using chemical vapor deposition（CVD）.Then,the atom-level contact between the Pt（111）surface and the Mo₂C（001）surface is realized via the combination of wet reduction and low-temperature annealing,resulting in the Pt_11.7/Mo₂C and Pt_6.4/Mo₂C composite materials with highly combined degree between Pt and Mo₂C.Among then,when it compares with Pt/C,Pt_11.7/Mo₂C not only exhibits almost equivalent electrocatalytic activity but also owning higher stability.After electrochemical process for 30 h,Pt_11.7/Mo₂C showed only an electrochemical attenuation rate of 0.8%.This research provides ideas for the design of new composite materials to obtain high-efficiency electrocatalysts for crystal surface regulation.