Preparation And Electrocatalytic Water Splitting Of Efficient Transition Metal Phosphides

Hydrogen,as an ideal reproducible and clean pollution-free energy,has triggered great attention in the past years owing to the energy shortage and increasing environmental pollution concerns.Electrochemical water splitting is an attractive and low-cost technology for generating high-quality hydrogen with carbon neutrality.However,the sluggish reaction kinetics and high energy consumption of the hydrogen evolution reaction（HER）and the oxygen evolution reaction（OER）are some of the biggest challenges faced in water splitting technology.To overcome these challenges,considerable research has been devoted to exploring high-performance bifunctional electrocatalysts and minimizing the dynamic overpotential of the reactions.Although noble metals such as Pt and Ir-/Ru-based oxides are known to be highly efficient electrocatalysts for HER and OER,respectively,they suffer from high production cost,low abundance and insufficient stability,seriously hindering their large-scale and widespread commercial application.The construction of highly active and cost-effective non-noble metal bifunctional electrocatalysts has thus attracted significant attention for water splitting.Recently,transition metal phosphides（TMPs）with economically feasible and advantageous physicochemical properties have been extensively studied and considered as promising non-precious bifunctional electrocatalysts for water splitting.（1）Highly efficient and robust non-noble bifunctional electrocatalysts with good stability are essential for electrochemical water splitting（EWS）.Till now,there is still a major challenge for the large-scale application of EWS.Herein,we report a great strategy to design a novel hybrid nanostructure of Co₂P nanoparticles（NPs）uniformly capsulated with the ultrathin N,P-doped carbon layers,and then integrated into carbon cloth（N-Co₂P/NPC）.Benefiting from the electronic structure of Co₂P,the as-prepared water-splitting catalysts not only offers more active sites but also protects the catalysts from the degradation and agglomeration with high stability in alkaline electrolyte.As expected,the N-Co₂P/NPC catalyst exhibits outstanding catalytic activity,which only requires overpotentials of 68 and 230 m V to achieve 10 m A cm^-2 for HER and OER,respectively.Notably,the electrolyzer assembled by N-Co₂P/NPC consumes a cell potential as low as1.53 and 1.69 V(at 10 and 100 m A cm^-2,respectively),making a big improvement for the design and synthesis of highly efficient bifunctional catalysts for overall water splitting.（2）We selected bimetallic phosphate（Ni Co P）as the main material and systematically studied the role of doping in rare earth elements（Er,Nd,Ce,La,and Yb）in increasing the catalytic activity of HER and OER.The RE doped Ni Co P nanowire array on the nickel foam（NF）first prepares the metal phosphate pre-drive with a simple hydrothermal system,and then under simple low-temperature phosphate treatment.The experimental results show that Er-doped Ni Co P exhibits excellent HER and OER dual-functional activity,Er-Ni Co P/NF catalyst,which has an overpotential of 46 m V to drive HER and 225 m V for OER in the alkaline electrolyte at the current density of 10 m A cm^-2.The corresponding two-electrode system of the catalyst for water decomposition can drive a current density of 10 m A cm^-2 with a voltage of 1.51 V,which has nearly 100%Faraday efficiency and exhibits high stability.Further through electrochemical activity area,electrochemical impedance study and DFT calculation results revealed that the higher electrolytic water efficiency is mainly due to the following two aspects:（1）the synergy between the bimetallic enhances the conductivity,optimizes the reaction adsorption energy,thereby accelerating water splitting kinetics;（2）the appropriate Er incorporation into Ni Co P lattice can significantly modulate the electronic structure with the d-band centers of Ni and Co atoms by shifting to lower energies with respect to the Fermi level,improve the natural activity of the catalyst,accelerate the electron transmission rate and catalytic reaction dynamics,thus improving the electrocatalytic activity.There is no doubt that our work can provide new ideas for the rational design and development of inexpensive electrode materials for electrochemical applications with high catalytic properties.