TRANSITION METAL BASED ELECTROCATALYSTS FOR WATER SPLITTING

Electrochemical water splitting is a catalytic process in which water molecule can be catalytically reduced to dihydrogen in cathode and oxidized to oxygen molecule in anode. The electrical energy that is used for water splitting can be renewable when the energy source is sunlight, geothermal heat, tide, etc., and the hydrogen gas can thus be generated sustainably. Nonetheless, the hydrogen produced through electrochemical water splitting is less than 10% of the total amount.The top limitation of its wide applications is the low activity of catalysts in both cathodic reaction (hydrogen evolution reaction, HER) and anodic reaction (oxygen evolution reaction, OER). The dissertation covers heteroatoms doping strategy in activating HER and OER catalysts that I have developed in my PhD study. For instance, N doping has been found to create new facets and active sites of Ni3S2 that are able to improve the hydrogen adsorption. As a result, the overpotential of Ni3S2 can be decreased from 240 mV to 155 mV at 10 mA/cm2, while the TOF of N doped Ni3S2 can be increased as much as 2 times of the pristine Ni3S2. A carbon doping strategy was adopted to activate NiO water-alkali HER catalyst. Combined our experimental and theoreticality study, carbon doping has created under-coordinated Ni sites that are favorable for hydrogen adsorption. Meanwhile, the carbon dopant also serves as the “hot-spot” in water dissociation that contributes to the improved kinetics of HER. The carbon doped NiO showed an ultralow overpotential of 29 mV at 10 mA/cm2, even comparable with the benchmark Pt/C catalysts. On the other hand, Fe-doped β-Ni(OH)2 nanosheets supported on Ni foam were developed for OER and able to achieve a low overpotential of 219 mV at geometric area current density of 10 mA cm-2, and a high electrochemical surface area current density of 6.25 mA cm-2 at the overpotential of 300 mV. This high intrinsic catalytic activity should be due to the strong electron-withdrawing ability of Fe dopant that makes the adjacent Ni active in OER, as well as the unique mixed amorphous/crystalline heterogeneous structure as preferential adsorption sites towards OER intermediates