In recent years, hydrogen has drawn a lot of attention as a potential source of clean energy because it burns without producing climate-damaging emissions. But most of the world’s hydrogen is produced with a high associated carbon footprint. Alternative, cleaner methods are expensive and technically complex.
Now, a team of researchers from the University of Houston, the Chinese University of Hong Kong, and Central China Normal University have reported a significant advance, a two-electrode catalyst that relies on one compound to efficiently produce hydrogen and oxygen from both seawater and freshwater.
The team used a nickel/molybdenum/nitrogen compound, tweaked with a small amount of iron and grown on nickel foam to efficiently produce hydrogen and then, through a process of electrochemical reconstruction sparked by cycling voltage, converted to a compound that produced a similarly powerful oxygen evolution reaction.
Researchers said using a single compound for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) – although slightly changed through the reconstruction process – not only makes water splitting more affordable, it also simplifies the engineering challenges.
The new catalyst not only allows for efficient operations with a single catalyst but also works equally well in seawater and freshwater. “Compared with existing catalysts, this is on par with the best ever reported,” said Zhifeng Ren, a corresponding author of the paper.
Alkaline seawater was then systematically studied using the two-electrode catalyst. Due to the excellent seawater HER and OER activity of the individual catalyst, the electrolyzer exhibited record-high performance for seawater electrolysis, achieving a current density of 688 mA cm−2 at 1.7 V.
Further experiments under quasi-industrial conditions showed that the catalyst delivered a current density of 1000 mA cm−2 using just 1.56 volts in seawater. In addition, the stability testing of the catalyst showed that it exhibits good durability over 80 hours under harsh industrial conditions.
Most available catalysts work best in freshwater, but splitting seawater is more complicated, in part because of corrosion associated with the salt and other minerals. The new catalyst’s strong performance in seawater could solve this problem. It generates pure oxygen, avoiding the potential byproduct of corrosive chlorine gas produced by some catalysts.
“If you are making a device with two different materials on two electrodes, you have to figure out how the electric charge can flow through each electrode and design the structure to fit that,” said Shuo Chen, associate professor of physics at UH and co-corresponding author on the paper. “In this case, the material is not exactly the same because one (electrode) undergoes electrochemical reconstruction, but it is a very similar material, so the engineering is easier.”
- Minghui Ning, Fanghao Zhang, Libo Wu, Xinxin Xing, Dezhi Wang, Shaowei Song, Qiancheng Zhou, Luo Yu, Jiming Bao, Shuo Chen, and Zhifeng Ren. Boosting efficient alkaline fresh water and seawater electrolysis via electrochemical reconstruction. Energy Environ. Sci., 2022; DOI: 10.1039/D2EE01094A