Efficient development of catalytic materials requires knowledge of the decisive parameters defining the catalytic properties. In multicomponent metallic catalysts, these are categorized as electronic and geometric effects, yet they are strongly interrelated. A systematic disentanglement can be achieved by fixing one parameter while altering the other, which becomes possible through the substitution in isostructural intermetallic compounds. This approach enables the evaluation of electronic or geometric contributions both individually and combined. Herein, this is achieved by substitution of indium (three valence electrons) with tin (four valence electrons) in the series In1–x Sn x Pd2, which allows for a systematic variation of the total number of electrons per unit cell with only a minor variation of the unit cell parameters and thus the evaluation of the electronic effect. Geometric effects were evaluated by substitution of indium with gallium in the Ga1–x In x Pd2 series, which allows for a systematic variation of the interatomic distances while maintaining the same number of valence electrons per unit cell and close atomic coordinates. By substituting gallium with tin in the Ga1–x Sn x Pd2 series, both effects are combined and addressed simultaneously. The activity enhancement of the methanol oxidation reaction on the Ga1–x Sn x Pd2 series is attributed to the synergy of the combined effects.
The gradual substitution of one element by another from a different group in isostructural intermetallic compounds allows for a systematic variation of the total number of electrons per unit cell with only minor variation in geometric parameters. Thus, electronic (ligand) influences can be evaluated with only negligible geometric (ensemble) influences. Herein, the correlation between electronic and electrocatalytic properties in the methanol oxidation reaction (MOR) is investigated by increasing the valence electron count per formula unit through the substitution of indium (three valence electrons) in the isostructural series In1–x Sn x Pd2 by tin (four valence electrons). The MOR peak current densities show a distinct change in slope with varying substitution degrees. Within the reaction network for the oxidation of small organic molecules, it is suggested that the MOR mainly proceeds via CO (indirect path) when 0 ≤ x < 0.8 and via formate (direct pathway) when 0.8 ≤ x ≤ 1. The use of intermetallic compounds as platform materials opens perspectives into a fundamental understanding of electrocatalysis, which is a key issue for the effective development of catalysts for low-temperature methanol fuel cells and other relevant catalytic reactions.
Molybdenum–nickel materials are catalysts of industrial interest for the hydrogen evolution reaction (HER). Well-characterized surfaces of the single-phase intermetallic compounds Ni7Mo7, Ni3Mo, and Ni4Mo were subjected to accelerated durability tests (ADTs) and thorough characterization to unravel whether crystallographic ordering affects the activity. Their intrinsic instability leads to molybdenum leaching, resulting in higher specific surface areas and nickel-enriched surfaces. These are more prone to form Ni(OH)2 layers, which leads to deactivation of the Mo–Ni materials. The crystal structure of the intermetallic compounds has, due to the intrinsic instability of the materials in alkaline media, no effect on the activity. Ni7Mo7, identified earlier as durable, proves to be highly unstable in the applied ADTs. The results show that the enhanced activity of unsupported bulk Mo–Ni electrodes can solely be ascribed to increased specific surface areas.
Besides activity and selectivity, the stability is of great importance in the development of catalysts for long-term applications. However, the lack of standardized stability protocols in electrocatalysis remains a fundamental hurdle hindering progress in the field by the lack of quantitative comparability of data in different studies. Herein, an electrochemical protocol to address the stability of bulk electrodes is developed. The protocol tests in situ and operando stability in the electrochemical methanol oxidation in alkaline media using the intermetallic compounds SnPd 2 and ZnPd 2 as test materials. Stability tests resulted in an equimolar mixture of 0.5 M methanol and 0.5 M KOH being the optimum composition of the electrolyte to obtain low corrosion rates and in ZnPd 2 being less stable than SnPd 2 . The reported protocol is a first, easy-to-do step to investigate the stability of electrode materials which is a prerequisite for application as well as a knowledge-based development of new electrode materials.
In this study, the modification of glassy carbon electrodes by potentiostatic pulsed deposition of platinum nanoparticles and potentiostatic pulsed polymerization of polyaniline nanofibers was investigated. During the preparation of the nano-composite materials, the control of the potentiostatic pulsed deposition and potentiostatic pulsed polymerization parameters, such as pulse potential, pulse width time, duty cycle, and platinum precursor concentration allowed the optimization of the size, shape, and distribution of the deposited Pt nanoparticles. It is noteworthy that the polymerization method, cyclic voltammetry method, or potentiostatic pulsed polymerization method show an important effect in the morphology of the deposited polyaniline (PANI) film. The obtained modified electrodes, with highly uniform and well dispersed platinum nanoparticles, exhibit good electrocatalytic properties towards methanol oxidation.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.