(a) Transmission electron microscopy (TEM) and (b) corresponding high-resolution TEM images of the FNS/NiSe composite. (c) The bright-field TEM image and EDX elemental mappings of Fe, Ni, and Se for the FNS/NiSe composite (Scale bar: 300 microns).Cheap and efficient water splitting to generate hydrogen and oxygen could underpin the development of a sustainable hydrogen economy in the future. But while water splitting is an attractive means of producing hydrogen, the oxygen evolution reaction (OER) is sluggish and requires a catalyst. Precious metal electrocatalysts are effective but expensive and resources are scare. Instead, research is focusing on more abundant alternatives such as nonprecious transition metals like iron (Fe), nickel (Ni), and cobalt (Co).
Researchers from Hong Kong Polytechnic University and its Shenzhen Research Institute have developed a hybrid electrode material based on transition metal selenides [Ma et al., Materials Today Chemistry 9 (2018) 133-139].
“Expensive noble metal-based electrocatalysts are normally used for OER, but we have proposed a simple method to produce a low-cost electrocatalyst,” explains researchers Sainan Ma and Yuen Hong Tsang.
The hybrid electrocatalyst NiSe and Fe4.4Ni17.6Se16 is formed through a one-step thermal selenization process of porous FeNi alloy foam. Analysis of the hybrid using high-resolution electron microscopy and elemental mapping indicate that Fe4.4Ni17.6Se16 is distributed equally throughout NiSe.
The self-supporting porous material is extremely durable and displays very promising catalytic activity in alkaline conditions. With low overpotentials of 242 mV and 282 mV, the electrocatalyst can achieve current densities of 100 mA cm-2 and 500 mA cm-2, respectively. These values compare well with most of the reports of OER electrocatalysts in alkaline electrolytes, say the researchers.
“The Fe4.4Ni17.6Se16/NiSe hybrid foam can be used directly as an OER electrode, while most existing electrocatalysts come in powder form, which is not stable when it is made into electrode,” point out Ma and Tsang.
The researchers believe that it is the three-dimensional porous physical structure of the Fe4.4Ni17.6Se16/NiSe hybrid foam that is key to its catalytic prowess. They suggest that heterointerfaces in the hybrid material induce metal-rich defects, which facilitate absorption of oxygen ions and the formation of O-OH bonds, central to the OER. Moreover, the porous nature of the hybrid allows efficient and effective release of O2 bubbles generated during the electrochemical process.
“We believe this material will have practical application because the durability is good and the cost is relatively low compared with the noble metals based catalysts,” say Ma and Tsang.