Hierarchically Structured CoNiP/CoNi Nanoparticle/Graphene/ Carbon Foams as Effective Bifunctional Electrocatalysts for HER and OER

The rational assembly of multiple active components has been regarded as a feasible approach to constructing effective electrocatalysts for overall water splitting. In this work, we have first developed effective bifunctional electrocatalysts, namely, hierarchically structured CoNiP/CoNi nanoparticle/ graphene/carbon foams. Reduced graphene oxide nanosheets like papers encapsulate the backbones of carbonized melamine foams; meanwhile, numerous hybrid CoNiP/CoNi nanoparticles are dispersedly attached to the carbon matrix. These special structures endow electrocatalysts with excellent HER and OER performances. Their overpotentials of 224 mV and 341 mV can carry out the current density of 10 mA/cm2, and the corresponding Tafel slopes are 85 mV/dec and 58 mV/dec. Moreover, this electrocatalyst has good durability in the long term electrolysis of HER and OER. In the end, the role of each component in the HER and OER processes has been revealed. Well-dispersed nanoparticles function as the main roles owing to their rich active sites and desirable electronic structures. Graphene nanosheets not only provide good substrates for nanoparticles but also hinder the shrinkage of carbonized melamine foams. Besides, 3D carbon foams inserted with plentiful graphene nanosheets could construct interconnected conductive networks and hierarchical porous structures, promoting electron-transfer kinetics and enhancing mass-transfer efficiency. Therefore, partially doping P atoms can largely enhance the electrocatalytic performances of bimetal CoNi, and the conjugation of 2D graphene nanosheets and 3D carbon foams would be one promising candidate for electrocatalytic support. This work may deliver valuable guidance for exploiting high-performance electrocatalysts.