Rational Design And Performance Regulation Of Iron-group-based Electrocatalyts Towards Oxygen Evolution Reaction

The electrocatalytic decomposition of water driven by surplus electric energy is an effective way to obtain green hydrogen energy efficiently.The core reactions are hydrogen evolution reaction on cathode(HER)and oxygen evolution reaction on anode(OER).Nevertheless,the kinetics of both HER and OER are very slow and often require a higher overpotential to generate a larger current density,resulting in a lower efficiency in converting the overall electrical energy into chemical energy.While the use of conventional noble metal electrocatalysts,such as IrO2/RuO2(OER)and Pt(HER),can reduce the overpotential for water decomposition reactions.However,precious metal materials tend to be expensive,have low natural reserves and have poor cycling stability,limiting the large-scale application of electrolytic water hydrogen production technology.Therefore,the design and development of cheap,efficient and stable non-noble metal electrocatalysts has become a hot spot in the field of chemical and material research.Iron-group-based transition metal phosphates are abundant and low cost in terms of elemental composition.In terms of physical and chemical properties,most of them have good electrical conductivity,high mechanical strength,unique electronic structure and abundant variable valence states,etc.,showing excellent HER and OER activities under acidic or alkaline conditions,and are considered to be the most promising electrocatalytic materials to replace precious metals.On this basis,a series of mixed metal phosphide electrocatalysts with adjustable composition and structure were constructed by using prussian blue frame materials as precursors,etching with necessary chemical orientation and subsequent thermal phosphating technology.The relationship between the composition-structure and electrocatalytic activity and stability of electrocatalysts is preliminarily revealed,the specific research contents are as follows:1.N-doped carbon armored mixed metal phosphide nanoparticles confined in N-doped porous carbon nanoboxes,a particle-in-box nanostructure,were synthesized from monodisperse Ni3[Fe(CN)6]2·H2O nanocubes through sequential conformal polydopamine coating,ammonia etching,and thermal phosphorization.The product exhibited electrocatalytic performances for the OER in 1.0 M KOH,delivering 10,100,and 250 mA/cm2 at overpotentials of 203,242,and 254 mV,respectively,with an Tafel slope of 38 mV/dec,and the long-term stability was also excellent.The enhanced electrocatalytic activity and stability may be attributed to the particle-in-box structure as a nanoreactor offering confined and effective reaction environment,the conductive N-doped porous carbon shell for fast charge and mass transport,the synergistic effect between multi-component metal phosphides for enhanced intrinsic activities,and the carbon protection layer to prevent/delay the catalyst core from deactivation.This combined particle-in-box and chainmail design concept for electrocatalysts is unique and advantageous,and may be readily applied to the general field of heterogeneous reactions.2.A highly active and stable OER electrocatalyst was designed and developed through a cobalt-induced intrastructural enhancement strategy combined with suitable electronic structure modulation.A carved carbon nanobox embedded with tri-metal phosphide was prepared from a uniform Ni-Co-Fe Prussian blue analogue nanocube by sequential NH3·H2O etching and thermal phosphorization.The sample exhibited remarkable OER activity in an alkaline medium,affording a current density of 10 mA/cm2 at an ultralow overpotential of 182 mV and displayed a small Tafel slope of 47 mV/dec,superior to the most recently reported prominent OER electrocatalysts.Moreover,it showed impressive electrocatalytic durability,increasing by approximately 2.7%of operating voltage after 24 h of continuous testing.The enhanced OER activity and stability are ascribed to the following reasons:favorable transfer of mass and charge provided by the porous carbon shell,synergistic catalysis originating from appropriate electronic structure modulation,more catalytically active sites available on the hollow structure,and chainmail catalysis resulting from the carbon protective layer.Figure[56]table[4]reference[147]...