Carbon nanobowls supported ultrafine iridium nanocrystals: An active and stable electrocatalyst for the oxygen evolution reaction in acidic media

Iridium single-atoms anchored on a TiO2 support as an efficient catalyst for the hydrogen evolution reaction

Single-atom catalysts (SACs) play a vital role in the hydrogen evolution reaction (HER) owing to the highly desirable atom efficiency and the minimal amount of precious metals. Herein, we use TiO2 nanosheets to anchor stable atomically dispersed iridium (Ir) to be used as a catalyst (Ir@TiO2) for the HER. The atomic dispersion of Ir on the TiO2 substrate is confirmed by aberration-corrected scanning transmission electron microscopy and it is anchored by numerous surface functional groups on abundantly exposed basal planes in TiO2. In acidic media, the Ir@TiO2 catalyst (1.35 wt% Ir) shows a low overpotential (41 mV at 10 mA cm-2), a small Tafel slope of 42 mV dec-1, and a decent durability for 1000 cycles of the HER with the polarization curve having only a 1 mV shift, which are comparable with those of a commercial Pt/C catalyst with 20 wt% Pt. This work paves a way to design Ir atomically anchored catalysts with low cost and high activity.

Water electrolysis: from textbook knowledge to the latest scientific strategies and industrial developments

Replacing fossil fuels with energy sources and carriers that are sustainable, environmentally benign, and affordable is amongst the most pressing challenges for future socio-economic development. To that goal, hydrogen is presumed to be the most promising energy carrier. Electrocatalytic water splitting, if driven by green electricity, would provide hydrogen with minimal CO2 footprint. The viability of water electrolysis still hinges on the availability of durable earth-abundant electrocatalyst materials and the overall process efficiency. This review spans from the fundamentals of electrocatalytically initiated water splitting to the very latest scientific findings from university and institutional research, also covering specifications and special features of the current industrial processes and those processes currently being tested in large-scale applications. Recently developed strategies are described for the optimisation and discovery of active and durable materials for electrodes that ever-increasingly harness first-principles calculations and machine learning. In addition, a technoeconomic analysis of water electrolysis is included that allows an assessment of the extent to which a large-scale implementation of water splitting can help to combat climate change. This review article is intended to cross-pollinate and strengthen efforts from fundamental understanding to technical implementation and to improve the 'junctions' between the field's physical chemists, materials scientists and engineers, as well as stimulate much-needed exchange among these groups on challenges encountered in the different domains.

Dehydrogenation of Cycloalkanes over N-Doped Carbon-Supported Catalysts: The Effects of Active Component and Molecular Structure of the Substrate

Efficient dehydrogenation of cycloalkanes under mild conditions is the key to large-scale application of cycloalkanes as a hydrogen storage medium. In this paper, a series of active metals loaded on nitrogen-doped carbon (M/CN, M = Pt, Pd, Ir, Rh, Au, Ru, Ag, Ni, Cu) were prepared to learn the role of active metals in cycloalkane dehydrogenation with cyclohexane as the model reactant. Only Pt/CN, Pd/CN, Rh/CN and Ir/CN can catalyze the dehydrogenation of cyclohexane under the set conditions. Among them, Pt/CN exhibited the best catalytic activity with the TOF value of 269.32 h⁻¹ at 180 °C, followed by Pd/CN, Rh/CN and Ir/CN successively. More importantly, the difference of catalytic activity between these active metals diminishes with the increase in temperature. This implies that there is a thermodynamic effect of cyclohexane dehydrogenation with the synthetic catalysts, which was evidenced by the study on the activation energy. In addition, the effects of molecular structure on cycloalkane dehydrogenation catalyzed by Pt/CN were studied. The results reveal that cycloalkane dehydrogenation activity and hydrogen production rate can be enhanced by optimizing the type, quantity and position of alkyl substituents on cyclohexane.

Iridium Nanotubes as Bifunctional Electrocatalysts for Oxygen Evolution and Nitrate Reduction Reactions

One-dimensionally (1D) hollow noble meal nanotubes are attracting continuous attention because of their huge potential applications in catalysis and electrocatalysis. Herein, we successfully synthesize hollow iridium nanotubes (Ir NTs) with the rough porous surface by the 1-hydroxyethylidene-1, 1-diphosphonic acid-induced self-template method under hydrothermal conditions and investigate their electrocatalytic performance for oxygen evolution (OER) and nitrate reduction reactions (NO₃^-RR) in an acidic electrolyte. The unique 1D and porous structure endow Ir NTs with big surface areas, high conductivity, and optimal atom utilization efficiency. Consequently, Ir NTs exhibit significantly enhanced activity and durability for acidic OERs compared with commercial Ir nanocrystals (Ir c-NCs), which only require the overpotential of 245 mV to deliver the current density of 10 mA cm^-2. Meanwhile, Ir NTs also show higher electrocatalytic activity for NO₃^-RR than that of Ir c-NCs, such as a Faraday efficiency of 84.7% and yield rate of 921 μg h^-1 mg_cat^-1 for ammonia generation, suggesting that Ir NTs are universally advanced Ir-based electrocatalysts.