Electricity produced from renewable energy sources such as solar, wind, hydro, and marine power usually suffers from intermittency and storage capacities. Conversion of the electricity to chemical fuels for future use is an effective solution to overcome this limitation. Hydrogen (H2) is an ideal candidate to perform the role for its high gravimetric energy density. Electrolysis of water (H2O → H2 + O2) can easily achieve the conversion. However, the efficiency of electrochemical water splitting is largely impeded by the kinetic energy barriers for cathodic hydrogen evolution reaction (HER) and anodic oxygen evolution reaction (OER). Efficient electrocatalysts are urgently required to lower the overpotentials for HER and OER, thus improving the energy conversion efficiency and reducing the production cost of H2. In alkaline conditions, non-noble metal-based electrocatalysts have more chance to provide competitive activity as noble metal-based materials (Pt, Ir, Ru, and Pd).
In this Ph.D. thesis, Prussian blue analogues (PBAs) were explored as the precursors to synthesize active transitional metal-based electrocatalysts for HER and OER due to their controllable metal compositions, abundant CN groups, and easy preparation. In the first study, a bimetallic NiFeP layer coated on the NiP rods on Ni foam was successfully synthesized (NiFeP@NiP@NF). The self-supported and interfacial-connected structure favors mass transfer and reduces electrical resistance for electrocatalysis. The prepared NiFeP@NiP@NF is bifunctional for both OER and HER. In the second study, it is found that CoFe PBAs with different species (NH4+, K+) in the interstitial space can influence the composition, morphology, crystalline phases, and OER performance in 1.0 M KOH of their heat-treatment derivatives. The mechanisms of materials’ evolution, the OER catalytic performance, and materials’ properties were thoroughly explored.