Researchers at KTH Royal Institute of Technology in Stockholm have developed a new cost-effective electrocatalyst for water-splitting to produce hydrogen.
The monolayer of nickel–vanadium-layered double hydroxide shows a current density of 27 mA cm−2 (57 mA cm−2 after ohmic-drop correction) at an overpotential of 350 mV for water oxidation. This performance is comparable to those of the best-performing electrocatalysts that are composed of non-precious materials—nickel–iron-layered double hydroxides for water oxidation in alkaline media—the researchers report in an open access paper in Nature Communications.
The new catalyst also offers a competitive, cheap alternative to catalysts that rely on more expensive, precious materials, such as iridium oxide (IrO2) or ruthenium oxide (RuO2).
Water splitting is considered one of the most promising strategies to produce chemical fuels such as hydrogen. The half reaction of the water splitting process, water oxidation, remains the bottleneck of the whole process at present. Therefore, developing highly efficient water oxidation catalysts is crucial. Some precious metal-based electrocatalysts, such as IrO2 and RuO2, have shown excellent performance for water oxidation; however, they suffer from high-cost and relative scarcity of precious metals, which limits their applications. Although some first-row transition metal oxides (for example, NiOx, NiFeOx, CoOx and MnOx) had been developed as low-cost electrocatalysts for water oxidation, most of them still cannot compete with IrO2 and RuO2.
Recently, the earth-abundant Ni–Fe double-layered hydroxide (NiFe-LDH) catalysts have attracted attention … it is nowadays known as one of the most active catalysts with a low overpotential and high electrolysis current. Since then tremendous efforts have been devoted to further improve the activity of NiFe-LDH, such as exfoliation and hybridization, to the extent that LDH catalysts can now outperform IrO2 in alkaline media; however, the aforementioned methods are still too complicated for large-scale applications.
It is already known that Fe(III) incorporated in Ni(II)-based LDH is the key aspect for the high catalytic performance, although the role of Fe in LDH is still ambiguous. … Up until now, there has been no reported earth-abundant metal element that can outperform Fe incorporated Ni-based LDHs. Searching for an earth-abundant metal to form efficient Ni-based LDH comparable to NiFe-LDH is still the state-of-the-art in this area of energy research.
In this work, we incorporate another earth-abundant element into Ni(OH)2: vanadium, and succeed in forming NiV-LDH as an efficient catalyst for the water oxidation reaction. A simple one-step hydrothermal method is employed to synthesize NiV-LDH. Without need for exfoliation or hybridization with other materials, the resulting monolayer NiV-LDH catalyst exhibits comparable activity to the best-performing NiFe-LDH for water oxidation in alkaline electrolyte.—Fan et al.
The research team, led by KTH Professor Licheng Sun, had earlier developed molecular catalysts for water oxidation with an efficiency approaching that of natural photosynthesis. The new material, composed of common earth-abundant elements, could help change the economics of large-scale hydrogen fuel production.
This is the first time that the metal, vanadium, has been used to dope nickel hydroxide to form a water oxidation catalyst, and it works very well—even beyond our expectations. No doubt this material can greatly expand the scope of non-precious metal elements of electrocatalysts, and it opens new areas for water splitting.—lead author Ke Fan
The material possesses a layered structure with monolayer nickel-vanadium oxygen polyhedron connected together with a thickness below 1 nanometer. This monolayer feature not only increases the active surface area, but also enhances the electron transfer within the material, said researcher Hong Chen.
Professor Sun expects the research to “open a new area of low-cost water oxidation catalysts, featuring stability and efficiencies that equal or even surpass some of today’s best catalysts including RuO2 and IrO2.”
Ke Fan, Hong Chen, Yongfei Ji, Hui Huang, Per Martin Claesson, Quentin Daniel, Bertrand Philippe, Håkan Rensmo, Fusheng Li, Yi Luo & Licheng Sun (2016) “Nickel–vanadium monolayer double hydroxide for efficient electrochemical water oxidation” Nature Communications 7, Article number: 11981 doi: 10.1038/ncomms11981