Engineering topics

Adiga, Prajwal

Publications and source records attributed to Adiga, Prajwal.

4 records

DOE OSTI2022

Breaking $\mathrm{OER}$ and $\mathrm{CER}$ scaling relations via strain and its relaxation in $\mathrm{RuO}$ 2 (101)

Green hydrogen production from abundant water sources is an important component of renewable energy storage. Water oxidation catalysts are typically considered bound by adsorbate scaling relations, limiting their activity for the oxygen evolution reaction (OER) as well as selectivity between OER and the chlorine evolution reaction (CER) that compete in saline water streams. RuO 2 is highly active for both reactions, and recent measurements have shown the OER activity is greater on undercoordinated, high index facets compared to the lowest-energy (110) facet often studied. The growth of such orientations as epitaxial films, however, can result in appreciable strain and potential surface faceting via its relaxation. Here, we find the activity and selectivity towards OER and CER vary with thickness in epitaxial (101) RuO 2 thin films: OER activity decreases 4x as film thickness increases from 8 nm to 48 nm, while CER activity is comparable. Thus, strain and its relaxation can be used to break scaling relationships between OER and CER, highlighting the important role that defects play in selective oxidation processes on RuO 2 in chloride-containing media.

36 MATERIALS SCIENCE↗

DOE OSTI2021

Epitaxial oxide thin films for oxygen electrocatalysis: A tutorial review

Epitaxial thin films can offer unprecedented definition of an electrocatalyst surface, defining the crystallographic orientation, interaction with a current collector, and providing an atomically flat surface for quantitative spectroscopy yielding mechanistic insight. This review introduces experts in thin films to the important parameters of electrochemical setups, techniques, and methods for quantifying electrocatalytic activity and comparing it across the literature. Examples are drawn from the literature measuring oxygen electrocatalysis on epitaxial oxide thin films. Furthermore, we share best practices in the robust measurement of intrinsic activity of thin films, including methods of electrical contact and assessment of charge transport in situ. We conclude by highlighting recent insights from epitaxial films in understanding oxygen electrocatalysis.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2021

Contribution of the Sub-Surface to Electrocatalytic Activity in Atomically Precise La 0.7 Sr 0.3 MnO 3 Heterostructures

Electrocatalytic reactions are known to take place at the catalyst/electrolyte interface. Whereas recent studies of size-dependent activity in nanoparticles and thickness-dependent activity of thin films imply that the sub-surface layers of a catalyst can contribute to the catalytic activity as well, most of these studies consider actual modification of the surfaces. Here, in this study, the role of catalytically active sub-surface layers was investigated by employing atomic-scale thickness control of the La 0.7 Sr 0.3 MnO 3 (LSMO) films and heterostructures, without altering the catalyst/electrolyte interface. The activity toward the oxygen evolution reaction (OER) shows a non-monotonic thickness dependence in the LSMO films and a continuous screening effect in LSMO/SrRuO 3 heterostructures. The observation leads to the definition of an “electrochemically-relevant depth” on the order of 10 unit cells. This study on the electrocatalytic activity of epitaxial heterostructures provides new insight in designing efficient electrocatalytic nanomaterials and core-shell architectures.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2021

Understanding the Electronic Structure Evolution of Epitaxial LaNi1-xFexO3 Thin Films for Water Oxidation

Rare earth nickelates including LaNiO3 are promising catalysts for water electrolysis to produce oxygen gas. Recent studies report that Fe substitution for Ni can significantly enhance the oxygen evolution reaction (OER) activity of LaNiO3. However, the role of Fe in increasing activity remains ambiguous, with potential origins both structural and electronic in nature. Here, by utilizing a series of epitaxial LaNi1-xFexO3 thin films synthesized by oxygen-assisted molecular beam epitaxy, we report that Fe substitution tunes the oxidation state of Ni in LaNi1-xFexO3 and a volcano-like OER trend is observed with x = 0.375 being the most active. Spectroscopy and ab initio modeling reveal that the high-valent Fe3+? B-site cationic species strongly increases the transition metal (TM) 3d bandwidth via Ni-O-Fe bridges and enhances the TM 3d-O 2p hybridization, boosting the OER activity. Furthermore, pH-dependent electrochemical measurements suggest that the OER on LaNi1-xFexO3 involves a lattice oxygen-mediated mechanism.

LaNiO3, Fe substitution, charge transfer, lattice ↗