Hydrogen evolution at Ir-Ni bimetallic deposits prepared by galvanic replacement

A novel bifunctional catalyst for overall water electrolysis: nano IrxMn(1-x)Oy hybrids with L12-IrMn3 phase

A nano Ir_xMn_(1-x)O_y hybrid electrode with a L1₂-IrMn₃ phase was used as a bifunctional catalyst with ultra-low iridium loading for overall water electrolysis in an acid solution for the first time. The HER activity of the Ir_xMn_(1-x)O_y hybrid electrode not only exceeded that of IrO₂, but also exceeded that of Pt/C. The OER activity of the Ir_xMn_(1-x)O_y hybrid electrode also exceeded that of IrO₂.

Galvanic Deposition of Pt Nanoparticles on Black TiO2 Nanotubes for Hydrogen Evolving Cathodes

A galvanic deposition method for the in-situ formation of Pt nanoparticles (NPs) on top and inner surfaces of high-aspect-ratio black TiO2 -nanotube electrodes (bTNTs) for true utilization of their total surface area has been developed. Density functional theory calculations indicated that the deposition of Pt NPs was favored on bTNTs with a preferred [004] orientation and a deposition mechanism occurring via oxygen vacancies, where electrons were localized. High-resolution transmission electron microscopy images revealed a graded deposition of Pt NPs with an average diameter of around 2.5 nm along the complete nanotube axis (length/pore diameter of 130 : 1). Hydrogen evolution reaction (HER) studies in acidic electrolytes showed comparable results to bulk Pt (per geometric area) and Pt/C commercial catalysts (per mg of Pt). The presented novel HER cathodes of minimal engineering and low noble metal loadings (μg cm-2 range) achieved low Tafel slopes (30-34 mV dec-1 ) and high stability in acidic conditions. This study provides important insights for the in-situ formation and deposition of NPs in high-aspect-ratio structures for energy applications.

Atomic Structure-Free Representation of Active Motifs for Expedited Catalyst Discovery

To discover new catalysts using density functional theory (DFT) calculations, binding energies of reaction intermediates are considered as descriptors to predict catalytic activities. Recently, machine learning methods have been developed to reduce the number of computationally intensive DFT calculations for a high-throughput screening. These methods require several steps such as bulk structure optimization, surface structure modeling, and active site identification, which could be time-consuming as the number of new candidate materials increases. To bypass these processes, in this work, we report an atomic structure-free representation of active motifs to predict binding energies. We identify binding site atoms and their nearest neighboring atoms positioned in the same layer and the sublayer, and their atomic properties are collected to construct fingerprints. Our method enabled a quicker training (200-400 s using CPU) compared to the previous deep-learning models and predicted CO and H binding energies with mean absolute errors (MAEs) of 0.120 and 0.105 eV, respectively. Our method is also capable of creating all possible active motifs without any DFT calculations and predicting their binding energies using the trained model. The predicted binding energy distributions can suggest promising candidates to accelerate catalyst discovery.

Hydrogen Evolution Reaction on Iridium-Modified Nickel Foam Surfaces

This work reports on cathodic hydrogen evolution reaction (HER), studied on Ir-activated nickel foam materials, prepared through spontaneous and electrodeposition methods (examined in 0.1 M NaOH electrolyte). Both Ir modifications of Ni foam caused substantial improvement of the HER kinetics, as compared with those recorded for as-received and surface-activated nickel foam materials. Electrochemical examinations were conducted through AC impedance spectroscopy and quasi-steady-state cathodic polarization experiments. Significance of catalytic nature of Ir deposit and employed deposition methodology on the HER behavior of such-obtained Ni foam/Ir composites were discussed in detail by means of SEM/EDX spectroscopy analysis.

Oxygen Evolution Reaction at IrO2/Ir(Ni) Film Electrodes Prepared by Galvanic Replacement and Anodization: Effect of Precursor Ni Film Thickness

IrO2/Ir(Ni) film electrodes of variable Ni content have been prepared via a galvanic replacement method, whereby surface layers of pre-deposited Ni are replaced by Ir, followed by electrochemical anodization. Electrodeposition of Ni on a glassy carbon electrode support has been carried out at constant potential and the charge of electrodeposited Ni controlled so as to investigate the effect of precursor Ni layer thickness on the electrocatalytic activity of the corresponding IrO2/Ir(Ni)/GC electrodes for the oxygen evolution reaction (OER). After their preparation, these electrodes were characterized by microscopic (SEM) and spectroscopic (EDS, XPS) techniques, revealing the formation of Ir deposits on the Ni support and a thin IrO2 layer on their surfaces. To determine the electroactive surface area of the IrO2 coatings, cyclic voltammograms were recorded in the potential range between hydrogen and oxygen evolution and the charge under the anodic part of the curves, corresponding to Ir surface oxide formation, served as an indicator of the quantity of active IrO2 in the film. The electrocatalytic activity of the coatings for OER was investigated by current-potential curves under steady state conditions, revealing that the catalysts prepared from thinner Ni films exhibited enhanced electrocatalytic performance.