Probing the electronic properties of nickel oxide (NiO) as electrocatalyst for renewable and sustainable electrolytic hydrogen production

Implementation of renewable energy technologies is important in the development of a sustainable and carbon neutral society. However, renewable energy sources such as wind and solar energy are intermittent by nature and calls for efficient and reliable energy storage technologies. One such storage solution is hydrogen, which can be produced by alkaline water electrolysis (AWE). Hydrogen production through water electrolysis is carbon neutral when coupled to renewable energy sources, and is projected to be the energy storage medium of the future. Electrical energy is stored as chemical energy in hydrogen and can be readily transported and efficiently converted back to electrical energy at the end users when needed. Although AWE provides a carbon neutral way of producing hydrogen, the cost and efficiency of this technology impedes mass production and must be optimized. In particular the sluggish oxygen evolution reaction (OER), operating at high positive potentials put stringent demands on electrocatalyst material. This project thus emphasizes the oxygen evolution reaction (anode) by using earth-abundant nickel oxide (NiO) catalysts that are doped with iron (Fe). These catalysts, depending on synthesis technique, show promising performance and hold great potential to replace noble metal oxide electrocatalysts. An important result of the project is that iron added in the electrolyte has a more significant effect on the catalytic activity than iron added during catalyst synthesis. In addition other types of Ni-based catalysts, such as Ni-Pt-Al compositions, have been investigated and optimized to a performance similar to that of PEM electrolysers.

The project has resulted in novel, optimized catalysts and a deeper understanding of the role of iron in nickel-iron catalysts. These results will be utilized in subsequent projects pursuing energy-efficient catalysts for energy storage as hydrogen.

Clean renewable energy technologies are gaining ground in an effort to ensure energy security whilst reversing the harmful effects of current high-carbon content technologies. One such a technology, that has the potential of being a zero-carbon emitting technology, is alkaline water electrolysis (AWE) coupled to renewable energy supplies such as wind and solar. Wind and solar energy can therefore be captured and stored as hydrogen for re-use at a later stage. The hurdle that needs to be overcome, to enable this technology to become mainstream, is that the oxygen evolution reaction (OER) on the anode of the electrolyser needs to be enhanced. This is done by employing a suitable electrocatalyst. Expensive iridium-based electrocatalysts are currently employed, however, earth-abundant nickel oxide (NiO) and iron (Fe) doped NiO, show a lot of promise, and depending on the synthesis technique has been proven to outperform the iridium-based electrocatalyst. Understanding why this is the case, will allow us to design and develop even better electrocatalysts. Conducting, amongst other characterisation techniques, X-ray photo-electron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS) on differently prepared samples of NiO and Fe-doped NiO, will serve to elucidate the electronic structure and density of states as well as the resistance of the NiO samples respectively. By employing different synthesis techniques, different samples of NiO and Fe-doped NiO will be obtained that exhibit different degrees of activity towards the OER. By conducting both physical and electrochemical characterisation on these samples, the contribution of physical and electronic properties to activity are to be deconvoluted. Laboratory activity does not, however, directly translate into commercial scale activity. To that regard the best performing samples are to be tested on a pilot AWE facility that employs membraneless technology that is at the forefront of development.