Cobalt based phosphide/metal nanohybrids for electrocatalytic water splitting in alkaline solution

Molecular hydrogen (H2) is a clean and sustainable energy carrier that has the potential to meet the ever-growing global energy demands at no environmental cost. Water splitting is one of the most promising ways to produce hydrogen but it is a thermodynamically uphill reaction and thus requires external energies such as electricity to initiate the reaction. Efficient water splitting requires highly active, earth-abundant and robust catalysts to promote the two half reactions, namely the hydrogen evolution and oxygen evolution reactions (HER and OER). Cobalt phosphides have been shown to be active toward HER, especially in acidic medium, and OER in alkaline medium. However, they show much inferior HER activity in alkaline medium due to the extra water dissociation step. Thus it is still a challenge to improve the catalytic activity of cobalt based phosphides for both HER and OER in alkaline solution. My thesis is focused on the nanohybridization of metal with phosphide for enhancing water splitting activity in alkaline medium and the mechanism of their performance. This thesis contains 5 chapters. Chapter 1 mainly introduces electorcatalytic water splitting, the development of cobalt based phosphides as electrocatalysts, nanohybridization and the objectives of my thesis. Chapter 2 introduces the techniques used in my experiments. Major findings of my study are presented and discussed in chapter 3 and 4. And the conclusions and outlooks are shown in chapter 5. In chapter 3, to increase the electrocatalytic HER activity of cobalt phosphide in alkaline solution and figure out the mechanism, I synthesized 3D porous Co-P/Co nanohybrids nanosheets array grown on carbon cloth. This catalyst showed efficient HER performance in alkaline medium. It showed a low overpotential (128 mV at 10 mA cm-2), low Tafel slope (58 mV dec-1), and prominent electrochemical stability. Moreover, it exhibited superior activity and stability than Co-P/CC. Most im