Enhanced electrocatalytic oxygen evolution activity in geometrically designed SrRuO3 thin films

Adiga

et al. 2021

Small

the redox of these metals during cycling, such as in RuO 2 [14] and Ni-based oxides, [15] can be used to estimate their surface concentration. The density of active sites is often simply approximated by the exposed geometric surface area (measured by, e.g., microscopy or N 2 adsorption [16] ) or the electrochemical surface area (ECSA) by assumptions regarding intrinsic capacitance. [15,[17][18][19] However, all of these normalization approaches imply that electrochemical activity is governed exclusively by the terminal surface layer of the oxide, without serious consideration of sub-surface layers that may influence activity as well.Size effects in the OER activity of nanoparticles, [20,21] thickness-dependent effects in thin films, [22] and substrate-dependent effects in 2D materials [23] imply that while a catalytic reaction occurs at the catalyst/electrolyte interface, the supporting layers of a catalyst (and/or its support) can influence activity as well. For oxides, these size effects can include manipulating the ability of transition metal sites to oxidize prior to the onset of OER. [20,21] Thickness effects can additionally include charge transfer to/from a support, [24][25][26] quantum tunneling through ultra-thin layers, [27,28] and formation of a 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. In this study, the role of catalytically active sub-surface layers was investigated by employing atomicscale 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.The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/smll.202103632.

Section: Resultsmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

Contribution of the Sub‐Surface to Electrocatalytic Activity in Atomically Precise La_0.7Sr_0.3MnO₃ Heterostructures

Adiga

et al. 2021

Small

ACS Appl. Energy Mater.

“…Hydrogen is regarded as one of the cleanest fuels for the future, and its energy efficient production by water splitting is identified as an important goal of the emergent science and technology. − Among the different available routes, electrochemical water splitting process is a technically attractive and potentially viable solution . It involves oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) at the two electrodes, and both these reactions require efficient and robust catalysts.…”

Section: Introductionmentioning

confidence: 99%

Faceted Colloidal Metallic Ni₃N Nanocrystals: Size-Controlled Solution-Phase Synthesis and Electrochemical Overall Water Splitting

Shanker

Ogale

2021

Self Cite

We report a size-tunable synthesis of faceted Ni3N nanocrystals (NCs) at low temperatures (210–230 °C) via a solution processing route for the first time and demonstrate their viability as an efficient electrocatalytic material for overall water splitting. The high carrier density of Ni3N NCs combined with the faceted morphology is shown to render a broadband absorption in the infrared range attributed to the energy-dispersed localized surface plasmon excitation. The Ni3N NCs show an efficient electrocatalytic activity with impressively low overpotentials of ∼74 and 142 mV for the hydrogen evolution reaction (HER) and 190 and 270 mV for the oxygen evolution reaction (OER), with current densities of 10 and 100 mA/cm2, respectively. The Tafel slopes for HER and OER are 49 and 56 mV/dec, respectively, which are quite small. Furthermore, these Ni3N NCs require a small voltage of 1.48 V to produce a current density of 10 mA/cm2 for overall water splitting conducted in an alkaline electrolyzer when they are used both as a cathode and an anode.

“…As a catalyst in the varied electrochemical processes, single-crystalline transition metal oxide (TMO) thin films have been intensively investigated because of their precise-controllable surface stoichiometry and long-range lattice ordering, which enables us to obtain its link to the consequent catalysis performance. − In the oxygen evolution reaction (OER), the surface absorption/desorption and the charge transfer properties between the TMO and oxygen intermediates (including OOH*, OH*, and O*) are determined by the 3d electronic structure and its coupling/interaction strength. − Conventionally, the decoration of the 3d electronic structure can be established by A-site chemical doping, − oxygen vacancy, − strain, − and so on . Among them, strain is believed to be a promising approach to modulable catalysis performance as the strong correlation between itinerant charge and crystal field.…”

mentioning

confidence: 99%

Ambipolar Enhanced Oxygen Evolution Reaction in Flexible van der Waals LaNiO₃ Membrane

Liu

et al. 2022

ACS Catal.

The atomic-level catalysis mechanism of various electrochemical processes can be achieved via the perovskite transition metal oxide (TMO) thin film with accurate stoichiometry and lattice ordering, which boosts the design and engineering of further promising catalysts. In the oxygen evolution reaction (OER), owing to the correlation nature of the TMO, strain can effectively tune the OER performance by modulating the electron occupancy and strengthening the exchange/coupling. However, the surface strain condition declines along with the rapid release of the interfacial lattice mismatch in conventional rigid TMO thin film. This not only restricts obtaining the most prominent strain tunability toward OER but also hinders understanding the fundamental mechanism. Here in this study, we have employed a van der Waals LaNiO 3 (LNO) membrane to determine the in situ strain effect on OER performance. We found that the OER activity is dramatically improved with both compressive and tensile strains exhibiting an ambipolar trend. Under only 0.2% compressive and tensile strains, the current densities are, respectively, enhanced ∼121% and ∼92% at 400 mV overpotential, compared with the unstrained LNO scenario. The weakened Ni−O chemisorption and enhanced charge transfer of LNO under varied strain conditions are responsible for this OER enhancement.