Probing the intrinsic activity heterogeneity at single metal oxide particles using nano impact electrochemistry and confined fluorescence electrochemical microscopy
Hatem Amin, Ruhr University Bochum, Bochum, GermanyKristina Tschulik, Ruhr University Bochum, ,
Transition metal oxide catalysts have recently gained special interest in water splitting and fuel cell applications due to their relatively high abundancy and high catalytic activity. However, the catalytic performance has typically been studied using the ensemble method, that is by immobilizing a large number of these particles on a current collector/support and measuring only their integral activity. In such ensemble studies, the catalytic response can be disturbed by many external factors, e.g., the use of binders and conducting supports, different resulting porosity or catalyst accessibility and non-optimal iR corrections, impeding a direct comparison of nanocatalysts.[1] On the other hand, single-entity electrocatalysis by the “nano impact” approach have been applied to probe the intrinsic activity of nanoparticles (NPs) at the individual particle level.[2] Herein, we demonstrate how the nano impact method can be used to quantify the intrinsic OER activity of cubic Co3O4 NPs. Furthermore, catalyst-support effects are investigated and showed higher activity for Pt support than carbon.[3] Importantly, the facet-dependent OER activity on spinel Co3O4 was successfully probed at the ensemble and single particle level by comparing the activity on spheroids ((001) and (111) facets) and cubes ((001) facets only).[4] In contrast to the tentative differences in OER activity recorded on ensembles, the single particle studies unambiguously reveal that Co3O4 cubes are more active than spheroids when both NPs have otherwise identical parameters. This enables the identification of highly active facets to guide shape-selective syntheses of improved metal oxide nanocatalysts for water oxidation. Additionally, spectro-fluorimetric electrochemistry can provide spatial resolution of the interface and can thus image the electrode heterogeneity.[5] By tracking the local pH changes accompanying HER and ORR at catalytic interfaces, the reaction layer and activity heterogeneity can be visualized. Hence, this approach opens an avenue to establish structure-activity relationships for industrially relevant catalytic processes. References [1] N. Blanc, C. Rurainsky, K. Tschulik, J. Electroanal. Chem. 872(2020)114345 [2] A. El Arrassi, Z. Liu, M. V. Evers, N. Blanc, G. Bendt, S. Saddeler, D. Tetzlaff, D. Pohl, C. Damm, S. Schulz, K. Tschulik, J. Am. Chem. Soc. 141 (2019) 9197 [3] Z. Liu, M. Corva, H.M.A. Amin, N. Blanc, J. Linnemann, K. Tschulik, Int. J. Mol. Sci. 22 (2021)13137. [4] Z. Liu, H. M.A. Amin, Y. Peng, M. Corva, R. Pentcheva, K. Tschulik, submitted. [5] J. Pruchyathamkorn, M. Yang, H. M.A. Amin, C. Batchelor-McAuley, R. G. Compton, J. Phys. Chem. Lett. 8 (2017) 6124