Water splitting reaction for green hydrogen gas production improved

The problem of (oxy)hydroxide's poor electrical properties has been a long-standing challenge towards the achievement of efficient water splitting. Now, a team of researchers led by Associate Professor Junhyeok Seo from the Department of Chemistry at Gwangju Institute of Science and Technology, have found a solution to this issue in the form of Schottky junctions.

In a recent study made available online on 30 August 2023 and to be published in Volume 340 of the Applied Catalysis B: Environmental journal in January 2024, they demonstrated an electrode with Schottky junction formed at the interface of metallic nickel-tungsten nitride (Ni-W₅N₄) and semiconducting n-type nickel-iron (oxy)hydroxide (NiFeOOH) catalyst. This electrode was able to overcome the conductance limit of (oxy)hydroxide and improved the water splitting ability of the setup.

Notably, two materials, a metal and a semiconductor, with largely different electronic behaviors were put in contact to make an energy difference at the interface, forming a junction. "Our research utilized this potential energy barrier present in the Schottky junction to accelerate electron flow in the electrode, leading to a significant increase in oxygen evolution reaction activity, expediting overall water splitting," explains Dr. Seo, highlighting the core mechanism behind their newly designed electrode.

Upon carrying out electrocatalytic water splitting, the team observed that Ni-W₅N₄ alloy catalyzed the hydrogen evolution reaction, resulting in 10 mA/cm² current density at a small overpotential of 11 mV. Furthermore, the rectifying Schottky junction formed at the interface of Ni-W₅N₄|NiFeOOH nullified the non-conductive lamination produced by (oxy)hydroxide species. In forward bias, it exhibited a current density of 11 mA/cm² at 181 mV overpotential. The electrochemical analysis of the electrode revealed that the improved catalytic activity could indeed be attributed to the Schottky junction.

Lastly, the researchers designed an electrolyzer using their Schottky junction electrode for industrial seawater electrolysis. They found that the new device could operate continuously for 10 days, while also exhibiting outstanding catalytic activity and durability during electrolysis. It showed a remarkable current density of 100 mA/cm² at an overpotential of just 230 mV.

Overall, the researchers believe that these findings can contribute toward a sustainable strategy for hydrogen production to eventually replace conventional methods that still rely on fossil fuels. As Dr. Seo concludes, "Freshwater and seawater are abundant and renewable sources of protons. Efficient water splitting systems ensure that we can establish sustainable production of zero carbon hydrogen fuel, thus helping manage our current climate problems."

Let us hope that the successful demonstration of Ni-W₅N₄|NiFeOOH electrode for water splitting opens up new avenues for Schottky junction-based durable and high-performance energy storage and conversion systems!