Selective electrochemical hydrogen evolution on cerium oxide protected catalyst surfaces. (1st May 2020)

• Record Type: Journal Article
• Authors: Endrődi, Balázs; Diaz-Morales, Oscar; Mattinen, Ulriika; Cuartero, Maria; Padinjarethil, Aiswarya Krishnakumar; Simic, Nina; Wildlock, Mats; Crespo, Gaston A.; Cornell, Ann
• Is Part Of: Electrochimica acta. Volume 341(2020)
• Publication Date: 2020-05-01
• Subjects: Cathode selectivity -- HER -- Industrial electrochemistry -- Chemical technology -- Dichromate; Electrochemistry -- Periodicals; Electrochemistry, Industrial -- Periodicals; 541.37
• DOI: 10.1016/j.electacta.2020.136022
• Languages: English
• ISSNs: 0013-4686

Abstract

Abstract: To date the only known solution to avoid the unwanted electrochemical reduction of hypochlorite and chlorate in industrial chlorate production, performed in undivided cells, is the addition of dichromate to the chlorate electrolyte. Because of the toxicity of this compound its use is restricted within the European Union to time limited authorization by REACH. Therefore, an alternative to sodium dichromate is essential to maintain, or even increase the process efficiency. The addition of cerium (III) salts to a hypochlorite solution increases the cathodic selectivity towards hydrogen evolution (HER), the preferred cathode process in industrial chlorate production. This is attributed to the deposition of a thin cerium oxide/hydroxide coating on the cathode, induced by the increased local alkalinity during electrolysis. Performing the electrodeposition of such protective coating ex situ, well-controlled coating thickness can be achieved. Optimizing the deposition conditions (time, current density), a coherent and stable coating is formed on the electrode surface. On this protected electrode surface the electrochemical reduction of hypochlorite is suppressed by ca. 90% compared to the bare Pt electrode, while the HER proceeds with high selectivity and unchanged kinetics. Interestingly, other electrochemical reactions (O2 reduction, H2 O2 reduction and oxidation) are also suppressed by the protective coating, suggesting that the deposited layer acts as an inorganic membrane on the electrode surface. Graphical abstract: Image 1 Highlights: Favoured H2 production (HER) over hypochlorite reduction upon Ce 3+ addition. The increased selectivity is attributed to a Ce-oxide/hydroxide coating formation. Ce-oxide/hydroxide coatings are electrodeposited galvanostatically ex situ. Fine-tuning the deposition conditions, stable CeOx coatings are formed. High HER selectivity in hypochlorite solutions using CeOx coated electrodes.