Pressure-promoted Synthesis Of Metal Phosphides And Carbides As OER Electracatalysts

Water splitting technology is widely recognized as an efficient and clean conversion and energy storage method,which is promising to alleviate energy shortage and environmental pollution problems.However,the complex electron transfers for oxygen evolution reaction(OER)severely limits the catalytic efficiency.Meanwhile,as the commercial OER catalysts,precious metals-based catalysts with high cost restrict the in-depth development of water splitting technology.The low-cost and high catalytic activity of transition metal compounds have attracted much attention,especially for transition metal phosphides and carbides,as a potential new type of catalysts,which have advantage of abundant,catalytic activity,adjustable function and stability.Current,the conventional methods for OER catalysts can obtain a perfect morphology,but the prepared catalysts often have problems such as complex composition and poor crystallinity,increasing the difficulty of understanding the catalytic mechanism.Therefore,in order to accurately identify the active sites and the catalytic mechanism,a facile and efficient synthesis method is essential to obtain a catalyst with high crystallinity and uniform structure.In this paper,we utilize a clean and rapid high-pressure(HP)synthesis to prepare pure and uniform chromium phosphides and bimetallic Co Mo P₂.Similarly,we have successfully synthesized preferred selections of transition metals doped Fe₃C@carbon nano-onions under HP,and studied their catalytic mechanism deeply.The prepared Polyphosphide-Cr P₄catalyst show a fluffy structure composed of a large number of nanoparticles,wihch is in favor of exposing more active sites and promoting charge transfer.Cr P₄catalyst has a low overpotential(?₁₀of 223 m V),fast kinetics(Tafel slope 49.7 m V·dec^-1),and long-term stability up to 60 h(10 m A·cm^-2)with the retention rate of 98%.Compared with P(3.66 e V),the Cr site has a lower?G_III(2.31 e V)and a higher affinity for water,making Cr as main active site showing great OER potential.During OER process,the adjustment of Cr P₄surface's structure makes Crⁿ⁺(3?n?4)transform into Cr³⁺,which induces the formation of intermediate(Cr³⁺OOH),boosting OER performance.The bimetallic phosphide Co Mo P₂nanoparticles show an excellent catalytic performance with?₁₀of only 270 m V and tafel slope of 50 m V·dec^-1.Moreover,there is almost no obvious current density attenuation after durability of 20 h(?₁₀of 270 m V),with retention rate of 99%.The surface Co atoms of Co Mo P₂have high catalytic activity,and partial Co have been reorganized to form Co(OH)₂further promoting OER.Mo atoms mainly play the role of adjusting the electronic structure and maintaining the structural integrity of Co Mo P₂.Moreover,a structural model after surface reorganization is constructed to evaluate and predict the OER of bimetallic phosphides.The 3d transition metals(Mn,Co and Ni)are respectively doped into Fe₃C to synthesize a high crystallinity and homogeneous Fe₃C-type crystal structure.The Co-doped Fe₃C@CNOs,having mesoporous nanostructures,exhibits an ideal OER with?₁₀of only271 m V.After the stability tested for 40 h(?₁₀₀of 400 m V),the retention rate of current density is more than 97%.The catalytic activity of Co-doped Fe₃C@CNOs is related to the synergy between Fe and Co atoms,but not the simple addition effect of non-simple Co and Fe atoms.Co atoms doped as the active site,can further reduce the rate-limiting step barrier((35)G_III)promoting OER performance.