Catalysts can usually greatly reduce the activation energy of electrolyzed water, thereby reducing the overpotential of electrolyzed water. The quality of the catalyst determines the total voltage required to electrolyze water and the conversion efficiency of electrical energy into hydrogen energy. For example, an electrolytic cell composed of two graphite electrodes usually requires a voltage greater than 2 V to produce hydrogen and oxygen, because graphite is not an ideal catalyst, while an electrolytic cell composed of two stainless steel electrodes requires a voltage of about 1.6-1.8V to produce hydrogen and oxygen. Hydrogen and oxygen. Researching new catalysts to increase energy conversion efficiency is a focus of great attention in the energy field.
In an acidic environment, platinum is a catalyst for the hydrogen evolution reaction. It has almost no overpotential and a very small Tafel slope (the additional voltage required to increase the current by 10 times), making it an almost ideal catalyst. , but due to the scarcity of platinum precious metal resources, scientists are looking for some cheap catalysts (transition metal sulfides, carbides and phosphides). Iridium oxide is a catalyst for the oxygen evolution reaction, but it also relies on scarce resources. At the same time, due to high potential and acidic environment, very few substances can simultaneously exhibit catalytic activity and stability for the oxygen evolution reaction, so so far no replacement for iridium oxide has been found. Taste.
In alkaline environments, platinum and iridium oxide are still good catalysts, but due to the stability of oxides and hydroxides in alkaline environments, there can be more low-atomic number transition metal compounds. choice. For example, nickel-based alloys exhibit excellent catalytic activity and stability for hydrogen evolution reaction, and nickel-iron-based composite materials and some perovskite materials exhibit excellent catalytic activity for oxygen evolution reaction.