Quasi-graphene-envelope Fe-doped Ni₂P sandwiched nanocomposites for enhanced water splitting and lithium storage performance

Developing advanced graphene-based composites is significant for the development of renewable green energy technology. Herein, we report a sandwich-like graphene-based composite (i.e., Fe-doped Ni₂P nanoparticles encapsulated by a graphene-like envelope), which is synthesized by the first polymerization of glucose (as a green carbon source) on the Fe-doped NiNH₄PO₄·H₂O nanosheet surface followed by high temperature annealing. The annealing process will crystallize the coated polymer into multilayer graphene, as the same time the Fe-doped precursor is decomposed into Fe-doped Ni₂P ((Fe)Ni₂P) nanoparticles encapsulated by the graphene envelope ((Fe)Ni₂P/graphene). When evaluated as a water splitting catalyst in acidic solutions, the graphene-encapsulated Fe-doped Ni₂P exhibits a low overpotential (∼50 mV) and a small Tafel slope (∼45 mV per decade) in 0.5 M H₂SO₄ solution. More importantly, the (Fe)Ni₂P/graphene composite shows an excellent stability in acid solutions in contrast to conventional Ni-based catalysts. On the other hand, owing to the structural advantage (i.e., efficient inner volume space for the nanoparticle expansion, high porosity for the electrolyte diffusion and high conductivity), the (Fe)Ni₂P/graphene nanocomposite exhibits a high specific capacity of 642 mA h g^-1 at 0.2 C and excellent cycling stability (93% retained after 200 cycles).