Water‐Splitting Electrocatalysis in Acid Conditions Using Ruthenate‐Iridate Pyrochlores

Abstract

The pyrochlore solid solution (Na 0.33 Ce 0.67 ) 2 -(Ir 1Àx Ru x ) 2 O 7 (0 x 1), containing B-site Ru IV and Ir IV is prepared by hydrothermal synthesis and used as a catalyst layer for electrochemical oxygen evolution from water at pH < 7. The materials have atomically mixed Ru and Ir and their nanocrystalline form allows effective fabrication of electrode coatings with improved charge densities over a typical (Ru,Ir)O 2 catalyst. An in situ study of the catalyst layers using XANES spectroscopy at the Ir L III and Ru K edges shows that both Ru and Ir participate in redox chemistry at oxygen evolution conditions and that Ru is more active than Ir, being oxidized by almost one oxidation state at maximum applied potential, with no evidence for ruthenate or iridate in + 6 or higher oxidation states.The electrochemical splitting of water is of significant relevance for contemporary energy applications, playing a key role in applications such as water-splitting electrolyzers for hydrogen production, and in reversible fuel cells for clean electricity production.

Hydrogen production from water electrolysis: role of catalysts

“…However, the requirement of acidic media limits the OER electrocatalysts to noble metal and noble metal oxide catalysts, which are the state-of-the-art OER electrocatalysts in the acidic media. This requirement leads to a high cost for the cell [ 27 ]. For the alkaline electrolysis cell, water splitting is performed under alkaline condition.…”

Ruthenium Oxide Nanosheets for Enhanced Oxygen Evolution Catalysis in Acidic Medium

“…Unlike hydrogen evolution, which involves transfer of two electrons, it requires four electrons, under high oxidative potential, to evolve oxygen. [6,7] In an acidic environment, however, only a limited number of OER catalysts are known to operate in a stable way. [4] However, the alkaline electrolytes have relatively low ionic conductivity [5] and are susceptible to accumulate carbonate as a contaminant by the reaction with carbon dioxide.…”

“…However, the alkaline electrolytes have relatively low ionic conductivity and are susceptible to accumulate carbonate as a contaminant by the reaction with carbon dioxide . Therefore, due to the higher ionic conductivity and fewer side reactions, proton exchange membranes (PEM) and acid solutions have been considered as electrolytes for application in various energy conversion devices such as PEM electrolyzers and reversible fuel cells . In an acidic environment, however, only a limited number of OER catalysts are known to operate in a stable way.…”

Observation of Mixed Valence Ru Components in Zn Doped Y2Ru2O7 Pyrochlores

“…14,15,16,17 The wide variety of ground states observed is due to the fact that Ru can be either in the 4+ or 5+ oxidation state, promoting good electrical and catalytic properties. 6,18 While the majority of the work has been done on materials in which the A site is fully occupied by either 3+ (Ru 4+ ) or 2+ (Ru 5+ ) cations, there are few studies reporting the effect of having a mixed oxidation state on the A site. 1,2 Doping the A sites with 2+ cations could result in a hole doping effect concomitant with an increased concentration of disordered oxygen vacancies in these oxides; 19,20,21,22,23 this is expected to provide them with the required ionic conductivity to be used as cathodes in IT-SOFC.…”