Rhenium-Based Electrocatalysts for Water Splitting

Due to the contaminationand global warming problems, it is necessaryto search for alternative environmentally friendly energy sources.In this area, hydrogen is a promising alternative. Hydrogen is evenmore promising, when it is obtained through water electrolysis operatedwith renewable energy sources. Among the possible devices to performelectrolysis, proton exchange membrane (PEM) electrolyzers appearas the most promising commercial systems for hydrogen production inthe coming years. However, their massification is affected by thenoble metals used as electrocatalysts in their electrodes, with highcommercial value: Pt at the cathode where the hydrogen evolution reactionoccurs (HER) and Ru/Ir at the anode where the oxygen evolution reaction(OER) happens. Therefore, to take full advantage of the PEM technologyfor green H-2 production and build up a mature PEM market,it is imperative to search for more abundant, cheaper, and stablecatalysts, reaching the highest possible activities at the lowestoverpotential with the longest stability under the harsh acidic conditionsof a PEM. In the search for new electrocatalysts and considering thepredictions of a Trasatti volcano plot, rhenium appears to be a promisingcandidate for HER in acidic media. At the same time, recent studiesprovide evidence of its potential as an OER catalyst. However, someof these reports have focused on chemical and photochemical watersplitting and have not always considered acidic media. This reviewsummarizes rhenium-based electrocatalysts for water splitting underacidic conditions: i.e., potential candidates as cathode materials.In the various sections, we review the mechanism concepts of electrocatalysis,evaluation methods, and the different rhenium-based materials appliedfor the HER in acidic media. As rhenium is less common for the OER,we included a section about its use in chemical and photochemicalwater oxidation and as an electrocatalyst under basic conditions.Finally, concluding remarks and perspectives are given about rheniumfor water splitting.