Effect of heat treatment on improving OER activity of NiFeOOH based aerogels: A combined experimental and theoretical study

Enhanced catalytic activity of oxygen evolution reaction (OER) catalysts is necessary to lower the cost of green hydrogen production. This study focuses on the use of a simple strategy of heat treatment to enhance the catalytic activity of NiFeOOH-based aerogels. The study shows that heat treatment of this aerogel at 150 °C leads to significant improvement in its catalytic activity, as evident in the staircase voltammetry results. To understand how heat treatment improves the catalytic activity, a DFT+U calculation was carried out on heat-treated and non-heat-treated catalysts. The calculation shows that the overpotential for OER decreases with heat treatment, which is related to the relative stability of the intermediates in heat-treated and non-heat-treated catalysts. Also, it has been found that heat treatment decreases work function, which might improve charge transfer and, thus, catalytic activity. Our calculations are in line with the experimental results that show the release of crystalline water at 150 °C which enhances the catalytic activity, and the formation of dense NiFeOx phase at higher temperatures which results in lower activity.