Bifunctional Hydrogen Evolution Reaction Catalyst for Solid-State Alkaline Water Electrolysis
Yanxin Li
Illinois Institute of Technology
Traditional fossil-based fuel has benefits us for more than 200 years, however, based on our current consumption rate, they will run out before 2100[1]. At the same time, combustion of fossil fuel creates CO2, which is also unknown as the greenhouse gas. Excessive CO2 gas has been released into the atmosphere since the Industrial Revolution and interfered heat being transferred out of the earth, in other words, caused global warming. As global warming appears to have a greater impact on our life, the demand of renewable, environmentally friendly, affordable and reliable alternatives to the traditional fossil-based fuel is expanding. Among many of the possibilities, hydrogen-based energy exhibits a potential to revolutionize energy production due to its clean nature. Hydrogen’s combustion product—pure water, does no harm to the surrounding environment, and it covers 71% of the earth surface[2]. The hydrogen economy starts with hydrogen production by water electrolysis; Hydrogen Evolution Reaction (HER), which is the reduction step in water electrolysis, plays a crucial role towards efficient and clean hydrogen generation. However, to date, large-scale industrial production of hydrogen in alkaline electrolyzers is constrained by low reaction kinetics even in the presence of platinum catalysts, otherwise known for its remarkable activity in acid environments. Therefore, in this research, substitute electrocatalysts will be synthesized and compared to Pt catalyst for HER activity.
The mechanism of water electrolysis involves two steps: the initial formation of hydrogen intermediates (H+[H2O]+e- ⇄Had-[+OH-]) and followed by the recombination step (2Had⇄H2) or an electron transfer step (H+[H2O]+e-+ Had⇄ Had-[+OH-]) involving water. The later step suggests the presence of a bifunctional catalyst with water splitting ability, in this case, Ni(OH)2/metal will improve the overall reaction[3]. Based on previous results obtained in ring disk electrode (RDE) by Danilovic et al., 2012, we will synthesize and evaluate the activity of Pt/C/ Ni(OH)2 electrocatalysts with different loadings of Ni(OH)2. Half-cell electrochemical experiments (RDE) will allow to determine the optimum composition of Ni(OH)2. The performance is measured in a solid-state alkaline water electrolyzer of the optimum catalyst (Pt/C/ Xwt%Ni(OH)2), with references to other Ni(OH)2 composition.
RDE experiments in 0.1M KOH have shown 20wt% Ni(OH)2 catalyst had the maximum activity for HER. For a RDE electrode with 1.8 ugPt/cm2, the HER activity (at 100 mV overpotential) increased 60% upon the addition of 20wt% Ni(OH)2. Electrolyzer experiments done with ultrapure water comparing Pt/C and Pt/C/20wt% Ni(OH)2 confirmed the RDE results. The cell voltage was 0.15 V lower in the case of 20wt% Ni(OH)2 electrocatalyst. Platinum metal group catalysts with Ni(OH)2 additives could be rewarding alternatives and reduce the costs if higher effectiveness in catalyzing hydrogen evolution reaction is steadily preserved. In other words, it might provide an accessible path to the clean hydrogen energy.
Reference
[1] Ecotricity. “The End of Fossil Fuels”. Ecotricity.co.uk
[2] "CIA – The world factbook". Central Intelligence Agency. Retrieved 20 December 2008.
[3] N. Danilovic, Ram Subbaraman. “Enhancing the Alkaline Hydrogen Evolution Reaction Activity through the Bifunctionality of Ni(OH)2/Metal Catalyst”. Angew. Chem. Int. Ed. 51, 1-5 (2012)
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