Oxygen Evolution Reaction on Tin Oxides Supported Iridium Catalysts: Do We Need Dopants?

Gabriel C Da Silva,Karl J J Mayrhofer,Seiti I Venturini,Mario Löffler,Siyuan Zhang,Serhiy Cherevko,Christina Scheu,Edson A Ticianelli

doi:10.1002/celc.202000391

Abstract

AbstractApplication of oxide supports is considered as a viable approach to decrease iridium loading in oxygen evolution reaction catalysis in acid electrolyte. While the most of the promising oxides are poor conductors, the need for doping is typically taken as granted, and a representative example is tin dioxide. There are still, however, serious concerns on the feasibility of this approach as we lack consensus on any activity gain by using such oxides, while doubts on stability are numerous. In this work, a set of catalyst/support combinations including two catalysts, viz. hydrous (IrOx) and rutile (IrO2) iridium oxides, and four supports, viz. SnO2 and Sb‐ (ATO), F‐ (FTO), and In‐doped (ITO) SnO2, are synthesized and characterized by a selection of complementary experimental techniques including rotating disk electrode and on‐line inductively coupled plasma mass spectrometry. It is found that the electrochemical activity in acid media of supported Ir catalysts is essentially the same, independent on presence or absence of dopants. Sb and In dopants are shown to be unstable and cause an increased dissolution of Sn. Besides, the degradation of the doped supports results in destabilization of iridium oxides. These results raise doubts on the real need for the use of dopants in SnO2‐based catalyst supports for electrochemical water splitting.

Highlights

The electrochemical splitting of water into hydrogen, hydrogen evolution reaction (HER) and oxygen, oxygen evolution reaction (OER), by means of water electrolysis is often pointed out as a viable solution to store the energy provided by intermittent renewable sources.[1]
After the heat treatment at 600 °C for 3 h, one can see that the compositions of rutile IrO2 materials (Table S2) are close to those obtained for the hydrous samples within the experimental error, evidencing no significant deviations from the expected amounts of iridium or dopants
SnO2, iridium oxide (IrOx)/fluorine-doped tin oxide (FTO) and IrOx/indium-doped tin oxide (ITO) catalysts compared to the unsupported IrOx material, while higher dissolution is detected for the

Summary

Introduction

Introduction technology.[2] In proton exchange membrane water electrolyzers (PEMWEs), Ir-based materials, in particular iridium oxide, are the state-of-the-art OER electrocatalysts due to the combination of their activity and stability.[3] due to the scarcity and high cost of iridium, its use in PEMWE must be optimized In this context, the use of catalysts supports have been suggested, since they can enhance the dispersion of the catalyst active phase, resulting in a higher electrochemically active area, allowing the reduction of the noble metal loading and of the cost of the PEMWE electrode.[3,4]. Carbon materials are the most widely used supports in electrocatalysis, because they combine the large surface area, high electrical conductivity, and adequate stability required, for example, in fuel cell applications.[5] In the anode of PEWME, the high potential in which the OER takes place may cause the oxidation of the carbon to CO2, making it unfeasible as a catalyst support To overcome this obstacle, the use of several electrically conductive oxides has been proposed.

Results

Discussion

Conclusion