Phase And Interface Regulation Of Iron Series(OXY)hydroxides And Their Performance For Electrocatalytic Water Splitting

Efficient alkaline electrocatalytic water splitting is one of the key technologies to realize sustainable large-scale hydrogen and oxygen production.At present,the materials with the highest electrocatalytic water splitting activities are precious metals.Although the noble metal-based catalysts have excellent catalytic performance,their high price hinder further applications.Iron series nano-materials have attracted extensive attention because of their advantages such as low price,earth abundance and high stability,which are considered to be electrocatalytic materials with great potential.In recent years,researchers have tried to use different strategies（regulation of size,morphology,composition and crystallinity）to improve the electrocatalytic properties of iron series nano-materials.However,there are still relatively few studies on the relationships between interface regulation and crystal phase regulation and the properties of iron series nano-materials.In this paper,iron series hydrogen（hydroxyl）oxides are studied.The phases and interface of these materials were regulated by a series of modification methods to improve their electrocatalytic water splitting performance.In order to study the preparation and oxygen evolution reaction（OER）properties of FeOOH nano-materials with different crystalline phases,single phase（α-,β-,δ-）and mixed-phase（α/β-,α/δ-,β/δ-）FeOOH nanostructures were successfully synthesized by solvothermal method according to the anion effects.Iodometric titration was applied to determine the concentration of oxygen vacancies in different crystalline phases and the OER activities were compared and analyzed.A comprehensive analysis of X-ray photoelectron spectroscopy and partial density of states（PDOS）calculation show that oxygen enriched vacancies in mixed-phase ofβ/δ-FeOOH can effectively improve the OER activity in alkaline solutions.The results of simulation calculation and electrocatalytic performance tests show of an optimized electronic structure and improved interface properties,exhibiting excellent OER performance and long-term stability.It can reach a current density of 10 m A cm^-2 with an overpotential of～180 m V,and can maintain for more than 30 hours at this current density.To study the synthesis of amorphous Ni（OH）₂ and its contribution to electrocatalytic hydrogen evolution（HER）and OER activity,crystalline-amorphous Ni-Ni（OH）₂ core-shell assembled nanostructures（c-Ni@a-Ni（OH）₂）were synthesized through a one-step thioacetamide（TAA）assisted electrodeposition method.Characterization results show that the hydrolysis process induced by TAA is critical for adjusting the composition of amorphous surface.Calculation results show that c-Ni@a-Ni（OH）₂ can strengthen the adsorption of catalytic intermediates（H*）on the surface,contributing to the electrocatalytic HER process.The current density simulation results show that the crystalline Ni core plays an important role in increasing the current density distribution on the amorphous nickel hydroxide shell.The prepared c-Ni@a-Ni（OH）₂ catalyst show high HER and OER activity and durability in 1.0 mol L^-1 KOH solution.In addition,when used as both the anode and cathode in 1.0 mol L^-1 KOH for overall water splitting（OWS）,c-Ni@a-Ni（OH）₂exhibits remarkable OWS activity with small overpotentials of 378 m V and 586 m V at 10 m A cm^–2 and 50 m A cm^–2,respectively.Moreover,c-Ni@a-Ni（OH）₂ also shows good OWS durability at least 24 hours.This work paves a new pathway for designing crystal-amorphous core-shell structural materials with controllable surface composition that can be used for energy conversion.To study the preparation of p-n heterojunction structure of CuO@CoOOH and its OER activity,the p-n heterostructure CuO@CoOOH nano-array electrocatalysts were successfully synthesized on copper foam（CF）in three steps（controlled in-situ oxidation etching,chemical bath deposition and in-situ anodization）.The p-n heterojunction can regulate the electronic properties of space charge region,thus promoting the electron transfer.In addition,in-situ Raman spectroscopy revealed that Co S_x in-situ anodizated into CoOOH with SO₄^2-adsorbed on the surface.The calculation of d-band density of states shows that the two-phase recombination enhances the adsorption of catalytic intermediates on the surface,and electron cloud density distribution simulation and DFT calculation show that the surface adsorbed SO₄^2-can promote the OER process by enhancing the adsorption of OH^-.The CuO@CoOOH p-n heterojunction with surface adsorbed SO₄^2-significantly enhance the OER performance and can reach a current density of 10 m A cm^-2 with an overpotential of～186 m V and can maintain for more than 100 hours.In addition,large-scale（14×25 cm²）samples have been successfully prepared,proving the prospect of industrial production.