Hydrogen evolution on Pt and polyaniline modified Pt electrodes—a comparative electrochemical impedance spectroscopy study

Why efficient bifunctional hydrogen electrocatalysis requires a change in the reaction mechanism

Hydrogen evolution reaction (HER) and hydrogen oxidation reaction (HOR) are both two-electron processes that culminate in the formation or consumption of gaseous hydrogen in an electrolyzer or a fuel cell, respectively. Unitized regenerative proton exchange membrane fuel cells merge these two functionalities into one device, allowing to switch between the two modes of operation. This prompts the quest for efficient bifunctional electrode materials catalyzing the HER and HOR with reasonable reaction rates at low overpotentials. In the present study using a data-driven framework, we identify a general criterion for efficient bifunctional performance in the hydrogen electrocatalysis, which refers to a change in the reaction mechanism when switching from cathodic to anodic working conditions. The obtained insight can be used in future studies based on density functional theory to pave the design of efficient HER and HOR catalysts by a dedicated consideration of the kinetics in the analysis of reaction mechanisms.

Mechanisms for hydrogen evolution on transition metal phosphide catalysts and a comparison to Pt(111)

Earth-abundant transition metal phosphides have been demonstrated to be promising alternative catalysts to replace Pt for hydrogen evolution reaction (HER). However, the mechanism for the hydrogen evolution reaction on transition metal phosphides remains unclear. Here, we explore the catalytically active sites and the reaction mechanisms on a variety of model transition metal phosphide surfaces by building cluster expansion models and running Monte Carlo simulations. We demonstrate that the effect of hydrogen coverage, interaction between hydrogen atoms and desorption kinetics all dictate the HER mechanisms and the active sites, and we propose mechanisms that are in good agreement with experimental studies. The present method provides a general and effective way to probe the active sites and study the mechanisms of catalytic reactions, which can facilitate the rational design of highly active electrocatalysts.

Determination of ascorbic acid using differential pulse voltammetry method on aniline-co-para–aminophenol modified electrode

The electro-synthesis of poly(aniline-co-para–aminophenol) on graphite electrode was examined using cyclic voltammetry (CV) over the potential window of −0.2 V to 1 V in phosphoric acid medium, which was comprised of potassium chloride and para–Toluene sulfonic acid (pTSA) as electrolyte support. Fourier transform infrared (FTIR) spectroscopy was employed to identify the electro-synthesized copolymer while impedance techniques were used to determine charge transfer resistance (Rct) in modified and unmodified electrodes. After this, the electro-catalytic effect of the modified electrode on ascorbic acid was examined using differential pulse voltammetry (DPV) and a very strong response was observed. A negative shift of about 0.33 V was found in the peak anodic potentials for ascorbic acid. Measurement using DPV indicated a proper response by the electrode to a wide range of ascorbic acid concentrations, from 0.0001 to 0.0004 M. The peak anodic currents for increased concentrations showed a proper linear range.