Influence of Composition and Nano-Scale Morphology on Enhancing the Acid Mediated Oxygen Evolution Electrocatalysis of Earth Abundant and Low PGM Containing Transition Metal Oxide Solid Solution Oxide Anodes

Abstract

Acid mediated proton exchange membrane based water electrolysis (PEMWE) is currently at the forefront amongst various hydrogen production approaches for harvesting clean and sustainable hydrogen fuel.1-4 In the present study density functional theory (DFT), based calculations were used to rationalize the thermodynamics and kinetics of OER. Accordingly, we identified and fabricated theoretically predicted earth abundant metal oxide (e.g. MnO2 and SnO2) based solid solution electrocatalysts comprising low precious group metal (PGM-Ir) as solute and 10 wt. % anionic dopant (F) [(Mn,Ir)O2:F, (Sn,Ir)O2:F] in one-dimensional (1D) architectures (nanorods and nanotubes)1, 5. The as-synthesized (Mn0.8Ir0.2)O2:10F and (Sn0.8Ir0.2)O2:10F systems demonstrated superior OER electrocatalytic performance (Fig. 1A-B) in comparison to the state-of-the art IrO2 and 2D thin films of corresponding compositions. The (Mn0.8Ir0.2)O2:10F and (Sn0.8Ir0.2)O2:10F anodes (at 1.45 and 1.5V, respectively) exhibited significantly lower charge transfer resistance (Rct ~ 2.5 and 4.2 Ω cm2, respectively). Furthermore, the systems exhibited higher electrochemically active surface area (ECSA ~ 704 and 38 m2g-1, respectively) and higher mass activity (40 and 21 Ag-1, respectively). In addition, they displayed significantly lower over-potential (200 and 285 mV, respectively) to deliver the benchmark current density of ~ 10 mAcmgeo 2 in comparison to pristine IrO2 and 2D thin films compositions of (Mn0.8Ir0.2)O2:10F and (Sn0.8Ir0.2)O2:10F. Such excellent OER performance of these systems is indeed attributed to the modified electronic structures of MnO2 and SnO2 following solid solution formation with IrO2 with incorporation of F. Additionally, the attributes of 1D nanostructures contribute to the improvement in electrochemical performance. These include high active specific surface area, high aspect ratio (L/D), high active-site densities, high roughness factor, lower charge transfer resistance (Rct) and high electronic conductivity with the presence of 1D channels, lattice planes with fewer crystal boundaries, presence of sufficient porosity and open space between the adjacent 1D channels enabling rapid release of oxygen gas. Durability tests conducted for 24h in 1N H2SO4 display minimal current density loss, indicating good electrochemical stability. Therefore, the as-synthesized 1D low PGM containing (Mn0.8Ir0.2)O2:10F and (Sn0.8Ir0.2)O2:10F electrocatalyst systems demonstrate promise as high performance and potentially low cost acid assisted PEM water splitting electrocatalyst systems. Results of these studies will be presented and discussed. Acknowledgements: Financial support of NSF-CBET grant# 1511390, Edward R. Weidlein Chair Professorship funds and the Center for Complex Engineered Multifunctional Materials (CCEMM) is acknowledged.