Strong negative nanocatalysis: oxygen reduction and hydrogen evolution at very small (2 nm) gold nanoparticles

Exploring the Role of the Connection Length of Screen-Printed Electrodes towards the Hydrogen and Oxygen Evolution Reactions

Zero-emission hydrogen and oxygen production are critical for the UK to reach net-zero greenhouse gasses by 2050. Electrochemical techniques such as water splitting (electrolysis) coupled with renewables energy can provide a unique approach to achieving zero emissions. Many studies exploring electrocatalysts need to "electrically wire" to their material to measure their performance, which usually involves immobilization upon a solid electrode. We demonstrate that significant differences in the calculated onset potential for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) can be observed when using screen-printed electrodes (SPEs) of differing connection lengths which are immobilized with a range of electrocatalysts. This can lead to false improvements in the reported performance of different electrocatalysts and poor comparisons between the literature. Through the use of electrochemical impedance spectroscopy, uncompensated ohmic resistance can be overcome providing more accurate Tafel analysis.

Au(111)@Ti6O11 heterostructure composites with enhanced synergistic effects as efficient electrocatalysts for the hydrogen evolution reaction

Developing cost-effective electrocatalysts for the hydrogen evolution reaction (HER) is of great significance for the renewable energy field. The Magnéli phase Ti_nO_2n-1 (4 ≤ n ≤ 10) has attracted much attention as a promising carbon-free support for electrocatalysts due to its high electrical conductivity and favorable electrochemical stability. Herein, we report the synthesis of a specific crystal-plane coupling heterostructure between Au(111) nanoparticles (NPs) and Ti₆O₁₁ by photoreduction. Benefitting from the modification of the electronic structure and synergistic effects of the heterostructure, the electron density around Au atoms is enhanced, and the Gibbs free energy of hydrogen absorption (ΔG_H*) was dramatically optimized to facilitate the HER process. The best electrocatalyst Au(111)@Ti₆O₁₁-50 exhibits a lower overpotential of 49 mV at a current density of -10 mA cm^-2 and a Tafel slope of 39 mV dec^-1 in 0.5 M H₂SO₄, and shows long-term electrochemical stability over 30 h. Au(111)@Ti₆O₁₁-50 shows a mass activity of 9.25 A mg_Au^-1, which is about 18 times higher than that of commercial Pt/C (0.51 A mg_Pt^-1). Meanwhile, the density functional theory (DFT) calculations suggest that the ΔG_H* of Au(111)@Ti₆O₁₁ is -0.098 eV, which is comparable to that of Pt (-0.09 eV). This work would be a powerful guide for the realization of efficient utilization of noble metals in catalysis.

Evaluation of the intrinsic catalytic activity of nanoparticles without prior knowledge of the mass loading

We propose a method enabling the evaluation of intrinsic catalytic activity of nanoparticles based on the diffusion-limited steady-state current.

An efficient ultra-thin chain-structured copper cobalt oxide/sulfide composite catalyst for electrochemical hydrogen generation

An ultra-thin chain-structured copper cobalt oxide/sulfide composite catalyst was prepared by hydrothermal method for HER.

Tailored gold nanostructure arrays as catalysts for oxygen reduction in alkaline media and a single molecule SERS platform

Although plenty of functional nanomaterials are widely applied in science and technology, cost-efficient, controlled and reproducible fabrication of metallic nanostructures is a considerable challenge. Automated electrorefining by scanning electrochemical microscopy (SECM) provides an effective approach to circumvent some drawbacks of traditional homogeneous syntheses of nanoparticles, providing precise control over the amount, time and place of reactant delivery. The precursor is just a raw metal, which is the most economically viable source. This approach ensures reproducibility and the opportunity for fabrication of micropatterns, which can be rapidly analyzed by scanning probe techniques. Here, a cost-effective methodology for the preparation of naked (ligand-free) metallic nanostructures, from polycrystalline gold using a moving microelectrode, is presented. Automated micropatterning of bare gold on indium tin oxide (ITO) demonstrates the versatility of this method to tune the size and shape of the nanostructures. The morphology of the obtained materials and thus their catalytic and plasmonic properties can be tuned using the electrorefining parameters. Programmable fabrication of sample microarrays by microprinting followed by comparative SECM studies or spectroscopic analysis allows quick optimization and characterization for specific purposes. Electrocatalytic oxygen reduction in alkaline media and surface-enhanced Raman spectroscopy (SERS) of single porphycene molecules are presented as model examples.

Recent Advances in Voltammetry

Recent progress in the theory and practice of voltammetry is surveyed and evaluated. The transformation over the last decade of the level of modelling and simulation of experiments has realised major advances such that electrochemical techniques can be fully developed and applied to real chemical problems of distinct complexity. This review focuses on the topic areas of: multistep electrochemical processes, voltammetry in ionic liquids, the development and interpretation of theories of electron transfer (Butler-Volmer and Marcus-Hush), advances in voltammetric pulse techniques, stochastic random walk models of diffusion, the influence of migration under conditions of low support, voltammetry at rough and porous electrodes, and nanoparticle electrochemistry. The review of the latter field encompasses both the study of nanoparticle-modified electrodes, including stripping voltammetry and the new technique of 'nano-impacts'.