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Diverse Ag–MnOx surface sites/structures in Ag–Mn electrocatalysts afford robust local electronic structures tuned for efficient oxygen reduction.

Improving electrocatalyst stability is critical for the development of electrocatalytic devices. Herein, we utilize an on-line electrochemical flow cell coupled with an inductively coupled plasma-mass spectrometer (ICP-MS) to characterize the impact of composition and reactant gas on the multielement dissolution of Mn(-Cr)-Sb-O electrocatalysts. Compared to Mn

Summary We report an active zinc-copper (Zn-Cu) bimetallic electrocatalyst for CO2 reduction to CO, prepared by a facile galvanic procedure. Under moderate overpotentials, Zn-Cu catalysts that are Zn rich exhibit intrinsic activity for CO formation superior to that of pure Zn, Cu, and Ag, the last of which is the state-of-the-art catalyst in CO2 electrolyzers. Combinatorial experiments involving catalysts prepared by physical vapor deposition reveal trends across the Zn-Cu system, corroborating the high CO selectivity unrivaled by other alloys and intermetallics. Physical and electrochemical characterization and first principles theory reveal that the origin of this synergy in intrinsic activity is an electronic effect from bimetallic Zn-Cu sites that stabilizes the carboxyl intermediate during CO2 reduction to CO. Furthermore, by integrating Zn-Cu into gas-diffusion electrodes, we demonstrate that bimetallic effects lead to improved electrocatalytic performance at industrially relevant currents. These insights provide catalyst design principles that can guide future development of efficient and earth-abundant CO-producing electrocatalysts.

The development of inexpensive and abundant catalysts with high activity, selectivity, and stability for the oxygen reduction reaction (ORR) is imperative for the widespread implementation of fuel cell devices. Herein, we present a combined theoretical-experimental approach to discover and design first-row transition metal antimonates as promising electrocatalytic materials for the ORR. Theoretically, we identify first-row transition metal antimonates – MSb2O6, where M = Mn, Fe, Co, and Ni – as non-precious metal catalysts with promising oxygen binding energetics, conductivity, thermodynamic phase stability and aqueous stability. Among the considered antimonates, MnSb2O6 shows the highest theoretical ORR activity based on the 4e− ORR kinetic volcano. Experimentally, nanoparticulate transition metal antimonate catalysts are found to have a minimum of a 2.5-fold enhancement in intrinsic mass activity (on transition metal mass basis) relative to the corresponding transition metal oxide at 0.7 V vs RHE in 0.1 M KOH. MnSb2O6 is the most active catalyst under these conditions, with a 3.5-fold enhancement on a per Mn mass activity basis and 25-fold enhancement on a surface area basis over its antimony-free counterpart. Electrocatalytic and material stability are demonstrated over a 5 h chronopotentiometry experiment in the stability window identified by Pourbaix analysis. This study further highlights the stable and electrically conductive antimonate structure as a promising framework to tune the activity and selectivity of non-precious metal oxide active sites for ORR catalysis.

Accurately quantifying applied potential is important to ensuring the comparability, accuracy, and precision of electrochemical studies. Reference electrodes (REs) enable knowledge/determination of the applied potential at electrodes in electrochemical systems. Ultimately, the choice of RE will depend on the particular requirements of a given electrochemical system, however, we note it is imperative to ensure the accuracy of the RE potential and its proper translation to a standardized scale. In this work, we highlight that while there are many commercially available REs, these must be experimentally calibrated to a reliable and practical standard potential scale, for instance the reversible hydrogen electrode (RHE) scale for aqueous systems. With representative data, we provide streamlined instructions on how to calibrate any RE to the RHE scale. We also provide guidance to mitigate and/or avoid possible electrolyte contamination issues arising from REs. Moreover, we offer a step-by-step guide on how to build a practical RHE RE, which may be a suitable and desirable option in certain applications. Our work emphasizes the need for the continuous adoption of standardized reference potential scales and demonstrates the versatility of the RHE scale, particularly in aqueous electrochemistry.

The oxygen reduction reaction (ORR) requires a large overpotential, which is a factor limiting the large-scale deployment of clean energy technologies such as hydrogen fuel cells (H2 FCs), direct methanol FCs, and metal-air batteries. Designing strategies to enhance catalyst activity, stability, and selectivity for the ORR is one method towards enhancing H2 FCs technology. Many predicted active catalysts are not stable in acidic media, resulting in limited catalyst options for standard proton exchange membrane H2 FCs. Some theoretically active, yet acid-unstable, catalysts, such as Ag, can be stabilized in alkaline media making anion exchange membrane (AEM) fuel cells an attractive alternative. Ag-rich catalysts are specifically ideal because of their low cost and Ag’s high abundance relative to other catalysts materials such as Pt. We have previously shown that Cu atoms in Ag-Cu alloys can be modified by Ag to produce an enhanced activity for the ORR at high Cu atomic loadings. Better understanding the nature of intrinsic enhancements for the ORR on alloys will help in the development of new ORR alloy electrocatalysts. Besides, Ag-Cu alloys, several other Ag-bimetallics (including Ag-Pd, Ag-Mn, Ag-Fe, and Ag-Co) have been predicted to be good catalysts for the ORR. Alloying could lead to activity enhancements via changes in electronic structure, strain, and/or localized geometry. The activity of Ag-based catalysts for the ORR needs to be enhanced. One strategy to do this is to alloy Ag, which binds oxygen adsorbates too weakly, to a metal such as Pd, which binds oxygen adsorbates too strongly and is also very active. In this work, we use a thin film model system to show intrinsic activity enhancements for the ORR on Ag-Pd catalysts, resulting in activities higher than those of both parent materials even after reducing the Pd content by half. Ag-Pd thin films of different compositions are prepared using electron beam physical vapor co-deposition. X-ray diffraction indicate alloying across the full compositional range tested and atomic force microscopy shows that the films are highly flat (roughness factor < 1.02). Electrochemical testing in 0.1 M KOH shows significant activity improvements for the Ag-Pd films. The films with +40 at% Pd have activities, at 0.9 V vs RHE, greater than the linear combination of pure Ag and Pd activities. On a Pd content basis, the thin films with +50 at% Pd exhibit higher kinetic current densities, at 0.9 V vs RHE, than both pure Ag and Pd. Ag10Pd90 is the most enhanced thin film, both on a surface area and Pd loading bases, demonstrating a 5-fold activity enhancement relative pure Pd. By correlating density functional theory with experimental activity and physical characterization measurements, we hypothesize that Ag is modifying Pd’s surface electronic structure to adsorb OH more weakly via ligand and strain effects. These enhanced Ag-Pd ORR catalysts could facilitate the large-scale implementation of efficient clean energy electrochemical systems such as fuel cells and metal-air batteries.