Preparation And Electrocatalytic Properties Of Phosphide And Metaphosphate Derived From Co-based Metal Organic Frameworks

The massive exploitation and use of fossil fuels has brought a huge energy and environmental crisis to the society.The development and utilization of low-cost,high-activity non-precious metal electrolysis catalysts to produce hydrogen is expected to bring opportunities to solve this problem.In recent years,transition metal phosphides and metaphosphates have become research hotspots due to their high hydrogen/oxygen evolution activity,good stability,and wide p H tolerance.However,the design of transition metal phosphide and metaphosphate catalysts with low loading,good electrical conductivity and long-term durability still faces huge challenges.Among them,transition metal metaphosphates are rarely reported,and their synthesis methods and performance are still great room for improvement.Therefore,in this paper,MOFs with high specific surface area and porous structure are used as precursors and sacrificial templates to prepare a series of transition metal phosphides and metaphosphates.Through element doping,phase modification and structure engineering,the electrochemical water splitting activity of the catalysts was further improved,and the catalytic mechanism was analyzed and studied in depth.The ternary pyrite-type cobalt phosphosulphide(Co PS)nanoparticles supported on nitrogen-doped carbon matrix(Co PS/N-C)were fabricated through carbonization and subsequent phosphosulfurization of Co-based zeolitic imidazolate frameworks(ZIF-67).The Co PS/N-C nanocomposites maintain the well-defined polyhedral structure as the pristine ZIF-67.Remarkably,Co PS/N-C nanocomposites exhibit promising electrocatalytic HER activity and stability in both acidic and alkaline electrolytes,affording a geometric catalytic current density of 10 m A·cm^-2at overpotentials of 80 and 148 m V vs.RHE,respectively.The existence of both P and S can tune each other's electronic properties substantially to produce an active catalyst phase,and play a key role in the adsorption and desorption of atomic H.A self-supported nanostructure consisting of Fe Co-Fe Co P@C encapsulated in nitrogen-doped carbon nanocages(denoted as Fe Co-Fe Co P@C@NCCs)were fabricated through a controlled carbonization and subsequent partial phosphorization process from core-shell Fe-Co PBAs@PDA hybrid precursor grown on carbon cloth(CC).Compared with Fe Co and fully phosphated Fe Co P,Fe Co-Fe Co P@C@NCCs formed under the optimal P content have the best HER and OER activity and stability in alkaline electrolytes.In addition,by employing the Fe Co-Fe Co P@C@NCCs as both the cathodic and anodic electrocatalysts,the designed alkaline electrolyzer only needs 1.64 V to deliver the required 10 m A·cm^-2 current density with an impressive durability of at least 48 h.The interconnected nanoarrays consisting of Co-Ni bimetallic metaphosphate nanoparticles embedded in carbon matrix(Co_2-xNi_xP₄O₁₂-C)were fabricated through a mild phosphorylating process of cobalt-nickel zeolitic imidazolate frameworks(Co Ni-ZIF).Among various Co_2-xNi_xP₄O₁₂-C catalysts with different Co:Ni ratios,Co_1.6Ni_0.4P₄O₁₂-C with optimal Ni content delivers a superior alkaline OER performance.The overpotential is only 230 m V at the current density of m A·cm^-2,as well as a small Tafel slope of 51 m V·dec^-1.DFT calculations and current density simulations indicate that the doping Ni sites can realize a suitable binding of oxygenated intermediates to the catalyst and the morphology integrity of interconnected nanoarrays can enhance the surface current density.Under the synergistic effect of these two effects,the OER activity of the Co_2-xNi_xP₄O₁₂-C nanoarray has a volcanic relationship with the amount of Ni doping,and the best catalytic performance can only be achieved when there is an appropriate amount of Ni doping.