Synthesis And Performance Of Carbon-Coupled Cobalt-Based Electrocatalysts For Oxygen Evolution Reaction

Electrocatalytic water splitting is perceived as an important clean energy conversion technology to produce hydrogen due to the advantages such as simple process,rich raw materials and high purity of hydrogen.Anodic oxygen evolution reaction?OER?,as an important half-reaction involved in electrocatalytic water splitting,has a sluggish reaction kinetics and requires a high overpotential because of the multistep four-electron-transfer pathway and several adsorption intermediates,leading to high energy loss of water splitting and further limiting the development and application of electrocatalytic water splitting technology.Therefore,the efficient and stable electrocatalysts are required in order to lower the overpotential of OER,thus reducing the overall energy consumption of water splitting.Layered double hydroxides?LDH?,which feature controllable composition,varied morphology and easy recombination,have been widely used in OER.However,the OER performance of LDH is seriously impeded by the poor conductivity and limited exposure of catalytic active sites.Therefore,how to design and fabricate electrode material with high electrocatalytic activity and conductivity is an urgent problem for LDH-based materials.Herein,the carbon-coupled cobalt-based LDH derivatives with high activity and stability were successfully fabricated by phosphating and chemical etching methods.Also,the corresponding electrochemical properties were investigated and the possible mechanism was revealed and decoupled.The detailed researches are as follows:The carbon coated iron-doped cobalt phosphide nanosheets?Fe-CoxP@C?were constructed by the low temperature phosphating method,where dopamine coated CoFe LDH acted as the precursor.Then,the effects of Fe doping and carbon layer for OER performance were investigated.It shows that the appropriate Fe doping can effectively enhance the electrocatalytic activity,while the surface-coated dopamine-derived carbon layer can not only efficiently stabilize the internal Fe-CoxP for the long-time catalysis,but also enhance the charge transfer ability of the catalysis and contribute to more exposed active sites.In 1 M KOH,Fe-CoxP@C nanohybrids can reach the current density of 10 mA cm^-2 at a low overpotential of 273 mV,with a small Tafel slope of 55 mV dec^-1,and keeps a nearly constant potential during 20-h testing at 10 mA cm^-2.The?-FeOOH/NiCo LDH-carbon integrated electrode was synthesized by the in-situ chemical etching/growth strategy,in which vertically oriented NiCo LDH nanoarrays grown on carbon fiber paper?LDH/CFP?was etched in an acidic environmental derived from the hydrolysis reaction of Fe³⁺,while?-FeOOH nanospindles were in-situ grown on NiCo LDH nanoarrays.The structure and composition of the materials during in situ etching/growth process for OER performance were investigated.Electrochemical results show LDH/CFP with the etching time of 30 s demonstrates the optimal OER performance in 1 M KOH,affording a low overpotential of 224 mV at 10 mA cm^-2,small Tafel slope of 38 mV dec^-1 and stable operation for 25 h at a high current density of 100 mA cm^-2 without obvious morphological changes.This superior performance is partially attributed to the synergistic catalytic effect between the in situ grown?-FeOOH nanospindles and the NiCo LDH nanosheets.While,the open structure derived from well-preserved LDH nanoarrays on interconnected CFP facilitates the rapid transport of electrolyte ions and the desorption of the produced oxygen.Moreover,the CFP substrate is favorable for the rapid electron transfer during the electrochemical OER process.