Post-Synthetic Immobilization of Ni Ions in a Porous-Organic Polymer-Graphene Composite for Non-Noble Metal Electrocatalytic Water Oxidation

A heterogeneous catalyst composite of graphene and porous-organic polymer, post-synthetically loaded with Ni-II ions, is reported. The microporosity of the composite was largely maintained after Ni impregnation. The composite has a very low Ni loading of 0.7 wt%, combined with an efficient electrocatalytic behavior towards water oxidation, as demonstrated by an onset potential of 1.51 V vs. RHE and a considerably low over-potential of approximate to 0.28 V. Moreover, a low overpotential of 0.4 V at current density of 10 mAcm(-2) was attained, and the composite shows also a high 100 mAcm(-2) current density for the OER at 1.8V vs. RHE. The Tafel slope for the Ni-loaded catalyst (45 mVdecade(-1)) indicates enhanced water oxidation characteristics as a result of the Ni ion loading. The Ni-loaded composite shows excellent durability in the water oxidation reaction, with enhanced performance upon progression of the cycles. This approach demonstrates the feasibility of fine tuning the composite's properties through post-synthetic impregnation with selected metal ions. The pyrimidine-based porous-organic polymer (PyPOP) provides a high surface area support with suitable anchoring sites for the catalytically active Ni ions, with the graphene layers providing the required electrical conductivity to the composite.