Boosting the hydrogen evolution reaction activity of Ru in alkaline and neutral media by accelerating water dissociation

Modulating Surface Cation Concentration via Tuning the Molecular Structures of Ethylene Glycol-Functionalized PEDOT for Improved Alkaline Hydrogen Evolution Reaction

The sluggish catalytic kinetics of nonprecious metal-based electrocatalysts often hinder them from achieving efficient hydrogen evolution reactions (HERs). Poly(3,4-ethylenedioxythiophene) (PEDOT) and its derivatives have been promising materials for various electrochemical applications. Nevertheless, previous studies have demonstrated that PEDOT coatings can be detrimental to HER performance. In this study, we investigated the alkaline HER efficiency of nickel foam coated with three types of ethylene glycol (EG)-functionalized EDOT. Specifically, EDOT derivatives bearing hydroxyl (-OH) and methoxy (-OCH3) end groups on the EG side chain and molecules containing two EDOT units are interconnected via EG moieties. EG groups are selected due to their strong interaction with alkali metal cations. Intriguingly, improved HER performance is observed on all electrodes coated with EG-functionalized EDOTs. Electrochemical impedance spectroscopy, electrochemical quartz crystal microbalance with dissipation, and XPS analysis are employed to explore the origin of enhanced HER efficiency. The results suggest the EG moieties can induce locally concentrated ions near the electrode surface and facilitate water dissociation through noncovalent interactions. The influence of EG chain length is systematically investigated by synthesizing molecules with di-EG, tetra-EG, and hexa-EG functionalities. This study highlights the importance of molecular design in modifying electrode surface properties to promote alkaline HER.

Understanding the Activation Mechanism of RhCrOx Cocatalysts for Hydrogen Evolution with Nanoparticulate Electrodes

Mixed oxides of Rh-Cr (RhCrOx), containing Rh3+ and Cr3+ cations, are commonly used as cocatalysts for the hydrogen evolution reaction (HER) on particulate photocatalysts. The precise physicochemical mechanisms of the HER at the catalytic sites of these oxides are not well understood. In this study, model cocatalyst electrodes, composed of nanoparticulate RhCrOx, were fabricated to investigate the physicochemical mechanisms of the HER. Electroanalytical and X-ray photoelectron spectroscopic measurements revealed that nanoparticulate RhCrOx produces reduced Rh (Rh0) species by maintaining an electrode potential more negative than 0.03 V versus the reversible hydrogen electrode (VRHE). This results in significant enhancement of the HER activity. The catalytic activity for the HER stems from the reduced Rh species, and the inclusion of Cr3+ (CrOx) aided in the electron transfer process at the solid/liquid interface, resulting in a higher current density during the HER. To achieve a solar-to-hydrogen efficiency of over 3%, the conduction band minimum of the particulate photocatalyst should be positioned more negatively than -0.10 VRHE. Moreover, the formation of electron trap states at potentials more positive than 0.03 VRHE should be avoided. This study highlights the importance of understanding the catalytic sites on metal oxide cocatalysts. Moreover, it offers a design strategy for enhancing the efficiency of photocatalytic water splitting.

Electrocatalytic Water Splitting: From Harsh and Mild Conditions to Natural Seawater

Electrocatalytic water splitting is regarded as the most effective pathway to generate green energy-hydrogen-which is considered as one of the most promising clean energy solutions to the world's energy crisis and climate change mitigation. Although electrocatalytic water splitting has been proposed for decades, large-scale industrial hydrogen production is hindered by high electricity cost, capital investment, and electrolysis media. Harsh conditions (strong acid/alkaline) are widely used in electrocatalytic mechanism studies, and excellent catalytic activities and efficiencies have been achieved. However, the practical application of electrocatalytic water splitting in harsh conditions encounters several obstacles, such as corrosion issues, catalyst stability, and membrane technical difficulties. Thus, the research on water splitting in mild conditions (neutral/near neutral), even in natural seawater, has aroused increasing attention. However, the mechanism in mild conditions or natural seawater is not clear. Herein, different conditions in electrocatalytic water splitting are reviewed and the effects and proposed mechanisms in the three conditions are summarized. Then, a comparison of the reaction process and the effects of the ions in different electrolytes are presented. Finally, the challenges and opportunities associated with direct electrocatalytic natural seawater splitting and the perspective are presented to promote the progress of hydrogen production by water splitting.

Phosphorous Doped Two-dimensional CoFe2O4 Nanobelt Decorated with Ru Nanoclusters and Co-Fe Hydroxide as Efficient Electrocatalysts Toward Hydrogen Generation

Developing efficient and durable hydrogen evolution reaction (HER) electrocatalysts has attracted considerable concerns for large-scale hydrogen generation. In this work, phosphorous doped two-dimensional (2D) CoFe2O4 nanobelt decorated with Ru and...

General fabrication of RuM (M = Ni and Co) nanoclusters for boosting hydrogen evolution reaction electrocatalysis

Rational design and fabrication of highly active electrocatalysts toward the hydrogen evolution reaction (HER) are of paramount significance in industrial hydrogen production via water electrolysis. Herein, by taking advantage of the high surface-to-volume ratio, maximized atom-utilization efficiency, and quantum size effect, we have successfully fabricated an innovative class of Ru-based alloy nanoclusters. Impressively, carbon fiber cloth (CFC) supported RuNi nanoclusters could exhibit outstanding electrocatalytic performance toward the HER, in which the optimal composition RuNi/CFC could achieve a current density of 10 mA cm^-2 with an overpotential of merely 43.0 mV in 1 M KOH electrolyte, as well as a low Tafel slope of 30.4 mF dec^-1. In addition to the high HER activity in alkaline media, such Ru-based alloy nanoclusters are also demonstrated to be highly active and stable in acidic solution. Mechanistic studies reveal that the alloying effect facilitates water dissociation and optimizes hydrogen adsorption and desorption, thereby contributing to the outstanding HER performance. This work paves a new way for the rational fabrication of advanced electrocatalysts for boosting the HER.