Comparative Analysis of Synthesis Routes for Antimony‐Doped Tin Oxide‐Supported Iridium and Iridium oxide Catalysts for OER in PEM Water Electrolysis

Abstract

The generation of H 2 is possible in different processes like the steam reforming of hydrocarbons, currently used in industrial processes or electrolysis of water. [1,2] In terms of electricity generation and utilization of H 2 as fuel in transportation, the latter approach seems to be opportune to minimize the reliance on fossil fuels and curb CO 2 -emissions. [1,3] With electrolysis, the generated H 2 could help establish a carbon-neutral transportation system. Additionally, in combination with fuel cells it can act as quasi-energy storage, both short-and long-term, to balance temporal disparities in the generation of renewable energy. [4][5][6] One implementation of water electrolysis is its proton exchange membrane (PEM) variant, which utilizes a protonconducting polymer membrane and noble-metal catalyst electrodes. [1] These catalysts are most often made from Pt on the cathode side and Ir on the anode. Noble metals are to some extent necessary here especially for the anode since the chemical environment presents harsh conditions and high oxidizing potentials, making most catalyst materials unstable long-term. Utilization of Ir comes with the downside of high investment costs, due to scarcity of Ir and therefore high price, which hinders the widespread application of PEM electrolysis systems. [1,3,6] In 2020 alone, the price of Ir tripled. [1,3] Reduction of the overall Ir content in PEM electrolysis systems is thus paramount for further industrial implementation. Recently, most employed catalysts consist either of metallic Ir, so-called Ir black or IrO 2 but these offer quite low volumetric activity, due to their nature as bulk catalysts. One strategy to reduce the Ir loading is to attach the catalyst to a conductive support material, quite similar to already applied fuel cell catalysts, with Pt supported on C. [7][8][9] In PEM electrolysis, the support also has to withstand harsh conditions, and thus the choice of material is drastically narrowed. Some metal oxides, like TiO 2 , are stable at the anode; however, their electrical conductivity is several orders of magnitude lower than that of bulk Ir; thus, the overall current efficiency is diminished. [7] Doping of the metal oxide lattice can alleviate the conductivity problem. One of the most promising candidates is antimony-doped tin oxide (ATO), which shows adequate electrical conductivity and stability. [10][11][12][13][14][15] Moreover, ATO might induce positive effects into Ir catalyst species, for instance, This study investigates and compares four different deposition methods for an iridium-based catalyst on antimony-doped tin oxide support for oxygen evolution reaction in water electrolysis. Different synthesis routes often lead to varying properties of the resulting catalyst and can result in performance disparities. Here, some of the most prominent methods are carried out on the same support material and evaluated with special focus on the deposition yield of Ir and thus cost efficiency along with electrochemical performance. The catalysts are als...

Wrinkled Ir-MnOx nanospheres as pH-universal electrocatalysts for oxygen evolution reaction

“…2d) of Ir-MnO x , the peaks at binding energies of 61.7 and 64.6 eV can be assigned to Ir 4f 7/2 and Ir 4f 5/2 of metallic Ir. 58,59 Relative to IrO x , metallic Ir may exhibit greater corrosion resistance and better conductivity, 60,61 which can reduce the OER overpotential to mitigate the peroxidation of MnO x . 62 Collectively, doping Ir into MnO x modulates the electronic structure of the resulting Ir-MnO x electrocatalysts, providing the possibility to optimize the adsorption of intermediates during the OER, and the MnO x supports provide robust anchor sites for highly active Ir species to increase the durability under harsh conditions.…”