Oxygen defect-rich double-layer hierarchical porous Co3O4 arrays as high-efficient oxygen evolution catalyst for overall water splitting

Construction of oxygen evolution electrocatalysts with abundant oxygen defects and large specific surface areas can significantly improve the conversion efficiency of overall water splitting.Herein,we adopt a controlled method to prepare oxygen defect-rich double-layer hierarchical porous Co3O4 arrays on nickel foam(DL-Co3O4/NF)for water splitting.The unique array-like structure,crystallinity,porosity,and chemical states have been carefully investigated through SEM,TEM,XRD,BET,and XPS techniques.The designated DL-Co3O4/NF has oxygen defects of up to 67.7%and a large BET surface area(57.4 m2g-1).Electrochemical studies show that the catalyst only requires an overpotential of 256 mV to reach 20 mA cm-2,as well as a small Tafel slope of 60.8 mV dec-1,which is far better than all control catalysts.Besides,the catalyst also demonstrates excellent overall water splitting performance in a two-electrode system and good long-term stability,far superior to most previously reported catalysts.Electrocatalytic mechanisms indicate that abundant oxygen vacancies provide more active sites and good conductivity.At the same time,the unique porous arrays facilitate electrolyte transport and gas emissions,thereby synergistically improving OER catalytic performance.

Electron-transfer enhanced MoO2-Ni heterostructures as a highly efficient pH-universal catalyst for hydrogen evolution

Hydrogen is one of the most promising energy carriers to replace fossil fuels and electrolyzing water to produce hydrogen is a very effective method.However,designing highly active and stable non-precious metal hydrogen evolution electrocatalysts that can be used in universal pH is a huge challenge.Here,we have reported a simple strategy to develop a highly active and durable non-precious MoO2-Ni electrocatalyst for hydrogen evolution reaction(HER)in a wide pH range.The MoO2-Ni catalyst exhibits a superior electrocatalytic performance with low overpotentials of 46,69,and 84 mV to reach-10 mA cm-2 in 1.0 M KOH,0.5 M H2SO4,and 1.0 M PBS electrolytes,respectively.At the same time,the catalyst also shows outstanding stability over a wide pH range.It is particularly noted that the catalytic performance of MoO2-Ni in alkaline solution is comparable to the highest performing catalysts reported.The outstanding HER performance is mainly attributed to the collective effect of the rational morphological design,electronic structure engineering,and strong interfacial coupling between MoO2 and Ni in heterojunctions.This work provides a viable method for the synthesis of inexpensive and efficient HER electrocatalysts for the use in wide pH ranges.