Measuring oxygen reduction/evolution reactions on the nanoscale
Amit Kumar,1 Francesco Ciucci,2 Anna N. Morozokvska,3 Sergei V. Kalinin,1 and Stephen Jesse1
1-Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN 37831
2-University of Heidelberg, Heidelberg, Germany
3-National Academy of Science of Ukraine, Kiev, Ukraine
Here we report direct measurements of oxygen reduction/evolution reactions and oxygen vacancy diffusion on oxygen-ion conductive solid surfaces with sub-10 nanometer resolution. In electrochemical strain microscopy (ESM), the biased scanning probe microscopy tip acts as a moving, electrocatalytically active probe exploring local electrochemical activity. The probe concentrates an electric field in a nanometer-scale volume of material, and bias-induced, picometer-level surface displacements provide information on local electrochemical processes. Systematic mapping of oxygen activity on bare and Pt-functionalized yttria-stabilized zirconia (YSZ) surfaces is demonstrated. The ESM approach allows direct visualization of these activation processes at the triple-phase boundary.
The overall performance of fuel cells is significantly limited by the activation of oxygen reduction and evolution reactions (ORR/OER). Despite the well-recognized role of oxygen reaction kinetics on the viability of energy technologies, the governing mechanisms remain elusive and until now, addressable only by macroscopic studies. This lack of nanoscale understanding precludes optimization of material architecture. ESM allows direct imaging of ORR/OER on the nanometer scale of individual structural elements, thus allowing the linking of the local functionality and advanced theoretical methods. The ubiquitous presence of electrochemical strains in virtually all ionic systems including fuel cells and memristive/electroresistive electronics suggest that ESM can be universally applied to these systems.
This research was conducted (A.K., S.J., S.V.K. ) at the Center for Nanophase Materials Sciences, which is sponsored at Oak Ridge National Laboratory by the Office of Basic Energy Sciences, U.S. Department of Energy. F.C. acknowledges the support from Marie Curie Reintegration Grant FastCell-256583. The authors are grateful to P. Rack and J. Fowlkes for deposition of Pt nanoparticles.
“Measuring oxygen reduction/evolution reactions on the nanoscale,” A. Kumar, F. Ciucci, A.N. Morozovska, S.V. Kalinin, and S. Jesse, Nature Chem. AOP, doi: 10.1038/nchem.1112