Journal
ADVANCED FUNCTIONAL MATERIALS
Volume 28, Issue 39, Pages -Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/adfm.201803712
Keywords
nickelates; oxygen evolution reaction; oxygen reduction reaction; oxygen vacancy; perovskite
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Funding
- U.S. Department of Energy (DOE), Office of Science, Early Career Research Program [68278]
- U.S. DOE, Office of Basic Energy Sciences, the Division of Materials Sciences and Engineering [10122]
- Ministry of Education, Singapore [MOE2014-T2-1-099]
- National Natural Science Foundation of China [11574365]
- Linus Pauling Distinguished Post-doctoral Fellowship at Pacific Northwest National Laboratory [PNNL LDRD69319]
- Office of Biological and Environmental Research
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Perovskite-structured (ABO(3)) transition metal oxides are promising bifunctional electrocatalysts for efficient oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). In this paper, a set of epitaxial rare-earth nickelates (RNiO3) thin films is investigated with controlled A-site isovalent substitution to correlate their structure and physical properties with ORR/OER activities, examined by using a three-electrode system in O-2-saturated 0.1 m KOH electrolyte. The ORR activity decreases monotonically with decreasing the A-site element ionic radius which lowers the conductivity of RNiO3 (R = La, La0.5Nd0.5, La0.2Nd0.8, Nd, Nd0.5Sm0.5, Sm, and Gd) films, with LaNiO3 being the most conductive and active. On the other hand, the OER activity initially increases upon substituting La with Nd and is maximal at La0.2Nd0.8NiO3. Moreover, the OER activity remains comparable within error through Sm-doped NdNiO3. Beyond that, the activity cannot be measured due to the potential voltage drop across the film. The improved OER activity is ascribed to the partial reduction of Ni3+ to Ni2+ as a result of oxygen vacancies, which increases the average occupancy of the e(g) antibonding orbital to more than one. The work highlights the importance of tuning A-site elements as an effective strategy for balancing ORR and OER activities of bifunctional electrocatalysts.
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