Non-Precious Transition Metal Based Electrocatalysts for Electrochemical Water Splitting


Student thesis: Doctoral Thesis

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Award date17 Aug 2020


In recent years, the problems of continuous fossil fuel consumption and uncontrolled greenhouse gas emission have driven intensive research on innovative technologies to generate clean energies through sustainable electrocatalytic water splitting. In water splitting, hydrogen and oxygen gases are typically generated via two half reactions, namely hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). As compared with HER, the high overpotential and the sluggish reaction kinetic of OER (4OH→ 2H2O + O2 + 4e-) have heavily restricted the efficiency of overall water splitting. Until now, Pt- and Ru/Ir-based noble materials are widely recognized as the most efficient electrocatalyst for HER and OER, respectively. Unfortunately, the high-cost, instability and scarcity of these noble metals significantly impede their practical utilizations.Detailed researches and results are listed as follows:

(1) A novel efficient and robust cobalt phosphate hydroxide (Co5(PO4)2(OH)4) prepared via a simple hydrothermal method for alkaline electrochemical OER. Importantly, the Co5(PO4)2(OH)4 catalyst exhibits a much lower overpotential of only 254 mV at a current density of 10 mA/cm2 on the glassy carbon electrode with a mass loading of 0.553 mg/cm2 and a small Tafel slopes of 57 mV/dec. Based on thorough structural analysis (e.g. XANES and XPS), the excellent electrocatalytic performance of Co5(PO4)2(OH)4 is resulted from its abundant electrochemical active sites exposed in the constituent zigzag edges of CoO6 octahedron, easier formation of active species in the distorted CoO6 structure as well as its outstanding hydrophilic characteristics. All these results can clearly confirm the metal phosphate hydroxides as a new type of stable electrocatalysts for the highly efficient oxygen evolution reaction.

(2) A superior bifunctional sandwich structure of an electrocatalyst, namely CoMnP/Ni2P/NiFe, toward both the HER and OER, in which the CoMnP nanosheets are prepared on hollow three-dimensional (3D) continuous nickel–iron (NiFe) foam via Ni2P bonding. It is notable that the hollow 3D substrate provides a high loading capacity of CoMnP nanosheets, while the continuous lowresistance Ni2P interlayer between the NiFe substrate and the CoMnP active material would yield an efficient electron transmission channel from the current collector to the active material. In addition, the introduction of Ni2P can modify the electronic structure of CoMnP via strong electron interaction as well as enhance the contact between the active material and the substrate. Importantly, the synergistic effect of combining surface and interface engineering in this unique sandwich structure gives a remarkable OER and HER performance, which can be proved using a 1.5 V battery to power an overall watersplitting device.

    Research areas

  • non-noble transition metal, Electrocatalyst, Hydrogen evolution reaction, Oxygen evolution reaction