Self-optimizing, highly surface-active layered metal dichalcogenide catalysts for hydrogen evolution

Low-cost, layered transition-metal dichalcogenides (MX_2) based on molybdenum and tungsten have attracted substantial interest as alternative catalysts for the hydrogen evolution reaction (HER). These materials have high intrinsic per-site HER activity; however, a significant challenge is the limited density of active sites, which are concentrated at the layer edges. Here we unravel electronic factors underlying catalytic activity on MX_2 surfaces, and leverage the understanding to report group-5 MX_2 (H-TaS_2 and H-NbS_2) electrocatalysts whose performance instead mainly derives from highly active basal-plane sites, as suggested by our first-principles calculations and performance comparisons with edge-active counterparts. Beyond high catalytic activity, they are found to exhibit an unusual ability to optimize their morphology for enhanced charge transfer and accessibility of active sites as the HER proceeds, offering a practical advantage for scalable processing. The catalysts reach 10 mA cm^(−2) current density at an overpotential of ∼50–60 mV with a loading of 10–55 μg cm^(−2), surpassing other reported MX2 candidates without any performance-enhancing additives

Cation insertion to break the activity/stability relationship for highly active oxygen evolution reaction catalyst

The production of hydrogen at a large scale by the environmentally-friendly electrolysis process is currently hampered by the slow kinetics of the oxygen evolution reaction (OER). We report a solid electrocatalyst α-Li2IrO3 which upon oxidation/delithiation chemically reacts with water to form a hydrated birnessite phase, the OER activity of which is five times greater than its non-reacted counterpart. This reaction enlists a bulk redox process during which hydrated potassium ions from the alkaline electrolyte are inserted into the structure while water is oxidized and oxygen evolved. This singular charge balance process for which the electrocatalyst is solid but the reaction is homogeneous in nature allows stabilizing the surface of the catalyst while ensuring stable OER performances, thus breaking the activity/stability tradeoff normally encountered for OER catalysts

Electrochemical Measurements as Screening Method for Water Oxidation Catalyst

In actual water splitting devices, the WOC will be deposited on an anode surface. Therefore, whatever the results obtained with WOC particles suspended in stirrer tank reactors, it becomes necessary to study WOC performances by means of electrochemical experimental setups. The WOCs deposition on an anode will depend on their physico-chemical nature, therefore several deposition methods, including wet and dry approaches, are found in literature. This Chapter reviews the available electrochemical techniques that can be adopted to study WOCs that are deposited on an electrode. In addition, the parameters used in literature to compare the different WOC materials will be explained. At the end of the Chapter, an example of the performance of different MnOx films will be reported. The water oxidation activity of three MnOx crystalline phases prepared by two deposition techniques will be compared. The aim of the comparison is to determine whether two electrodes having the same crystalline phase behave differently or not when they are deposited by two different techniques

Vulcan carbon as support for sputtered oxygen evolution electrocatalysts

The development of support structures for electrocatalysts has received a great deal of attention over the last decade, with carbon structures (i.e. nanostructures, Vulcan carbon (VC)) having been studied extensively. Carbon support structures increase the surface area, stability and activity of electrocatalysts in most cases, and can be used to overcome the delamination of thin films. In an attempt to (i) obtain surface structures and areas on SiO2 wafer pads, for combinatorial high-throughput sputtering and screening, that are comparable to glassy carbon (GC), (ii) eliminate delamination of the electrocatalyst and (iii) increase activity and stability, this study focused on VC:Nafion support preparation techniques. Four VC inks were prepared and used as carbon support on GC electrode inserts to analyse their effect on the activity of sputtered Ni thin films (40 nm) towards the oxygen evolution reaction (OER) in alkaline media. Linear sweep voltammetry (LSV) and chronopotentiometry (CP) were employed to compare the catalytic activity and stability of these sputtered Ni thin films on the various VC supports. Results suggest that similar activity compared with IrO2 and RuO2 could be achieved by sputtered Ni on VC:Nafion support, indicating improved Ni utilisation as well as improved short-term stability of the Ni thin films. These results validate the use of VC:Nafion support as substrate for sputtered electrocatalyst