The formation of PdZn bimetallic alloys on ZnO, TiO ₂ and Al ₂ O ₃ supports was investigated, together with the effect of alloy formation on the CO ₂ hydrogenation reaction. The chemical vapour impregnation (CVI) method produced PdZn nanoparticles with diameters of 3–6 nm. X-ray photoelectron spectroscopy and X-ray diffraction revealed the changes in the structure of the PdZn alloy that help stabilise formate intermediates during methanol synthesis. PdZn supported on TiO ₂ exhibits high methanol productivity of 1730 mmol kg _cat ⁻¹ h ⁻¹ that is associated with the high dispersion of the supported PdZn alloy.

The oxygen evolution reaction (OER) is crucial to future energy systems based on water electrolysis. Iridium oxides are promising catalysts due to their resistance to corrosion under acidic and oxidizing conditions. Highly active iridium (oxy)hydroxides prepared using alkali metal bases transform into low activity rutile IrO₂ at elevated temperatures (>350 °C) during catalyst/electrode preparation. Depending on the residual amount of alkali metals, we now show that this transformation can result in either rutile IrO₂ or nano-crystalline Li-intercalated IrO_x. While the transition to rutile results in poor activity, the Li-intercalated IrO_x has comparative activity and improved stability when compared to the highly active amorphous material despite being treated at 500 °C. This highly active nanocrystalline form of lithium iridate could be more resistant to industrial procedures to produce PEM membranes and provide a route to stabilize the high populations of redox active sites of amorphous iridium (oxy)hydroxides.

Eschewing the common trend towards use of catalysts comprising of Cu, it is reported that PdZn alloys are active for CO₂ hydrogenation to oxygenates. It is shown that enhanced CO₂ conversion is achievable through the introduction of Brønsted acid sites, which promote dehydration of methanol to dimethyl ether. We report that deposition of PdZn alloy nanoparticles onto the solid acid ZSM-5, via chemical vapour impregnation affords catalysts for the direct hydrogenation of CO₂ to DME. This catalyst shows dual functionality; catalysing both CO₂ hydrogenation to methanol and its dehydration to dimethyl in a single catalyst bed, at temperatures of > 270 ^oC. A physically mixed bed comprising 5% Pd 15% Zn/ TiO₂ and H-ZSM-5 shows a comparably high performance, affording a dimethyl ether synthesis rate of 546 mmol kgcat^-1 h^-1 at a reaction temperature of 270 ^oC.

Catalytic upgrading of CO₂ to value-added chemicals is an important challenge within the chemical sciences. Of particular interest are catalysts which are both active and selective for the hydrogenation of CO₂ to methanol. PdZn alloy nanoparticles supported on TiO₂ via a solvent-free chemical vapour impregnation method are shown to be effective for this reaction. This synthesis technique is shown to minimise surface contaminants, which are detrimental to catalyst activity. The effect of reductive heat treatments on both structural properties of PdZn/TiO₂ catalysts and rates of catalytic CO₂ hydrogenation are investigated. PdZn nanoparticles formed upon reduction showed high stability towards particle sintering at high reduction temperature with average diameter of 3–6 nm to give 1710 mmol kg⁻¹ h of methanol. Reductive treatment at high temperature results in the formation of ZnTiO₃ as well as PdZn, and gives the highest methanol yield.

The production of hydrogen through water electrolysis (WE) from renewable electricity is set to revolutionise the energy sector that is at present heavily dependent on fossil fuels. However, there is still a pressing need to develop advanced electrocatalysts able to show high activity and withstand industrially-relevant operating conditions for a prolonged period of time. In this regard, high entropy materials (HEMs), including high entropy alloys and high entropy oxides, comprising five or more homogeneously distributed metal components, have emerged as a new class of electrocatalysts owing to their unique properties such as low atomic diffusion, structural stability, a wide variety of adsorption energies and multi-component synergy, making them promising catalysts for challenging electrochemical reactions, including those involved in WE. This review begins with a brief overview about WE technologies and a short introduction to HEMs including their synthesis and general physicochemical properties, followed by a nearly exhaustive summary of HEMs catalysts reported so far for the hydrogen evolution reaction, the oxygen evolution reaction and the overall water splitting in both alkaline and acidic conditions. The review concludes with a brief summary and an outlook about the future development of HEM-based catalysts and further research to be done to understand the catalytic mechanism and eventually deploy HEMs in practical water electrolysers.