Hydrogen fuel acts as one of the most promising alternatives to petroleum fuels
owning to its high gravimetric energy density and environmental friendliness.
Hydrogen evolution reaction (HER), a half reaction of water splitting, plays a critical
role in producing high purity hydrogen fuels. Highly active and robust electrocatalysts
are required to decrease the overpotential, speed up the reaction rate, and thus to
minimize the overall energy consumption. In order to couple HER with OER to realize
overall water splitting in the same pH range, robust electrocatalyst is needed for high
efficient alkaline electrocatalysis. However, the activity of electrocatalyst in alkaline
medium is usually two to three orders of magnitude lower than that in acidic medium.
Thus, it is still a challenging issue to design earth-abundant electrocatalysts with low
cost, high activity and long-term stability and for HER from water splitting in alkaline
solutions.
Electrocatalytic property of Nickel was discovered almost a century ago, and over
the years, we have witnessed a continuous and rapid development in optimizing Ni-based
electrocatalysts. My thesis focuses on design of facile approaches for Ni material
modification by interfacing and nanostructuring of Ni metal, aiming to increase the
intrinsic activity as well as the active sites of Ni material for high-efficiency hydrogen
production. This thesis contains 5 chapters. Chapter 1 mainly introduces the
development of electrocatalysts for HER and the objects in my thesis. Chapter 2
introduces the experimental techniques employed in my research. Chapter 3 and 4 focus
on the findings in my study. The conclusion and outlook is shown in chapter 5.
In chapter 3, we report a facile synthesis route of three-dimensional porous Ni/Ni
3S
2
nano-interfaces on oxidized carbon cloth for HER in alkaline solution. This unique
structure exposes a high proportion of Ni/Ni
3S
2 hetero-interface to electrolyte, creating
a synergetic effect between Ni and Ni
3S
2 for enhancing HER. The synergetic effect at
the interface was verified by DFT calculation, which consists in an interface-assisted
heterolytic splitting of H
2O into OH
- and H
+, and the subsequent expeditious H
2-forming reaction owing to the weakened binding between Ni and H induced by the
neighboring Ni
3S
2. The resulting porous network shows a high HER activity in alkaline
media, reaching 10 mA/cm
2 at 95 mV with a tafel slope of 66 mV/dec, which is much
smaller than that of nickel metal currently being used in industry.
In chapter 4, We devised a facile electrodeposition strategy for growing Ni/MoO
x
heterostructure network on conductive substrate. By constructing Ni/MoOx interface,
the overpotential decrease to 122 mV at current density of 10 mA/cm
2, 62 mV lower
than that of Ni metal. We also found that Cu could greatly increase the activity of
Ni/MoO
x system as substrate. Comparing catalysts grown on Ni substrate and Cu
substrate, the Ni/MoO
x with Cu support manifests a factor of 3 activity increase in
catalysing HER, the overpotential further dropped to 42 mV at current density of 10
mA/cm
2. In addition to the synergetic effect between Ni and MoOx, we propose the
dramatic decrease of overpotential might be caused by Cu substrate, which might
probably play a role in optimization of hydrogen adsorption and desorption energy.
Chapter 5 gives the summary of my thesis and some outlook about the modification
of Ni-based mateirial in the future.
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