Separated hydrogen and oxygen evolution in alkaline water electrolysis
Recently, the iChEM researchers, Prof. Yonggang Wang, Prof. Yongyao Xia and their colleagues, reported a new alkaline water electrolysis technology with separated hydrogen and oxygen evolution. They successfully decoupled the hydrogen and oxygen production in alkaline water electrolysis by using nickel hydroxide as a redox mediator. In their architecture, the hydrogen production occurs at the cathode by water reduction, and the anodic Ni(OH)
2 is simultaneously oxidized into NiOOH. The subsequent oxygen production involves a cathodic NiOOH reduction (NiOOH-Ni(OH)
2) and an anodic OH- oxidization. Alternatively, the NiOOH formed during hydrogen production can be coupled with a zinc anode to form a NiOOH-Zn battery, and its discharge product (that is, Ni(OH)
2) can be used to produce hydrogen again.
Low-cost alkaline water electrolysis has been considered a sustainable approach to producing hydrogen using renewable energy inputs, but preventing hydrogen/oxygen mixing and efficiently using the instable renewable energy are challenging. The separate H
2 and O
2 production overcomes the challenge of H
2/O
2 mixing and facilitates the operation of alkaline electrolysis even with unstable power inputs. The separate H
2 and O
2 productions require different driving voltages (or input power), which implies that we can flexibly use sustainable energy, such as solar or wind power, with higher efficiency. For example, we can use solar energy at noon to drive the H
2-production step, which requires a high driving voltage (or power input), and solar energy at dusk to power the O
2-production step, which requires a low driving voltage. Finally, the combination of H
2 production and discharge of the NiOOH-Zn battery potentially provides a new energy storage/conversion approach for human life. For instance, solar energy can be used to drive the electrolysis to produce H2 during the daytime, and the discharge step of the NiOOH-Zn battery can be used to deliver energy to power electronic devices overnight.
The work is supported by the Natural Science Foundation of China (21333002, 21373060), Shanghai Science & Technology Committee (13JC1407900) and Collaborative Innovation Center of Chemistry for Energy Materials (2011•iChEM).
Link:
http://www.nature.com/ncomms/2016/160520/ncomms11741/full/ncomms11741.html
