Immobilization of functionalized iron(II) clathrochelates with terminal (poly)aromatic group(s) on carbonaceous materials and their detailed cyclic voltammetry study

Bis(formazanate) iron(II) complexes as cathode materials for one-compartment H2O2 fuel cells

In this paper, we describe the synthesis of two six-coordinate, pseudo(octahedral) bis(formazanate) Fe(II) complexes based on newly developed redox-active benzothiazole-substituted formazanate ligands. Complexes [FeII(L1)2], 1, and [FeII(L2)2], 2, were synthesized by reacting 1-(benzothiazol-2-yl)-5-phenyl-3-(pyren-1-yl)formazan (L1H) and 1-(benzothiazol-2-yl)-5-(2-benzoyl-4-chlorophenyl)-3-phenylformazan (L2H), respectively, with appropriate Fe(II) precursors at room temperature. The molecular structures of both bis(formazanate) iron complexes were established using single-crystal XRD, and other characterization methods were utilized to further characterize these complexes, as well as the newly synthesized ligands. Furthermore, the cyclic voltammetry studies of these compounds are documented, revealing that both complexes can undergo electrochemical reductions to create anionic and dianionic species. These complexes were further employed as cathodes in one-compartment membrane-less H2O2 fuel cells, operating in 0.5 M H2O2, with nickel foam serving as the anode. The maximum power densities achieved by the designed H2O2 fuel cells for complexes 1 and 2 were 1.88 mW cm-2 and 3.08 mW cm-2, respectively. This study demonstrates the significant potential of formazanate-based compounds in the development of cathode materials for H2O2 fuel cells.

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.

Graphene and Graphene-Like Materials for Hydrogen Energy

The review is devoted to current and promising areas of application of graphene and materials based on it for generating environmentally friendly hydrogen energy. Analysis of the results of theoretical and experimental studies of hydrogen accumulation in graphene materials confirms the possibility of creating on their basis systems for reversible hydrogen storage, which combine high capacity, stability, and the possibility of rapid hydrogen evolution under conditions acceptable for practical use. Recent advances in the development of chemically and heat-resistant graphene-based membrane materials make it possible to create new gas separation membranes that provide high permeability and selectivity and are promising for hydrogen purification in processes of its production from natural gas. The characteristics of polymer membranes that are currently used in industry for the most part can be significantly improved with small additions of graphene materials. The use of graphene-like materials as a support of nanoparticles or as functional additives in the composition of the electrocatalytic layer in polymer electrolyte membrane fuel cells makes it possible to improve their characteristics and to increase the activity and stability of the electrocatalyst in the reaction of oxygen evolution.

New types of the hybrid functional materials based on cage metal complexes for (electro) catalytic hydrogen production

Successful using of cage metal complexes (clathrochelates) and the functional hybrid materials based on them as promising electro- and (pre)catalysts for hydrogen and syngas production is highlighted in this microreview. The designed polyaromatic-terminated iron, cobalt and ruthenium clathrochelates, adsorbed on carbon materials, were found to be the efficient electrocatalysts of the hydrogen evolution reaction (HER), including those in polymer electrolyte membrane (PEM) water electrolysers. The clathrochelate-electrocatalayzed performances of HER 2H+/H2 in these semi-industrial electrolysers are encouraging being similar to those for the best known to date molecular catalysts and for the promising non-platinum solid-state HER electrocatalysts as well. Electrocatalytic activity of the above clathrochelates was found to be affected by the number of the terminal polyaromatic group(s) per a clathrochelate molecule and the lowest Tafel slopes were obtained with hexaphenanthrene macrobicyclic complexes. The use of suitable carbon materials of a high surface area, as the substrates for their efficient immobilization, allowed to substantially increase an electrocatalytic activity of the corresponding clathrochelate-containing carbon paper-based cathodes. In the case of the reaction of dry reforming of methane (DRM) into syngas of a stoichiometry CO/H2 1:1, the designed metal(II) clathrochelates with terminal polar groups are only the precursors (precatalysts) of single atom catalysts, where each of their catalytically active single sites is included in a matrix of its former encapsulating ligand. Choice of their designed ligands allowed an efficient immobilization of the corresponding cage metal complexes on the surface of a given highly porous ceramic material as a substrate and caused increasing of a surface concentration of the catalytically active centers (and, therefore, that of the catalytic activity of hybrid materials modified with these clathrochelates). Thus designed cage metal complexes and hybrid materials based on them operate under the principals of “green chemistry” and can be considered as efficient alternatives to some classical inorganic and molecular (pre)catalysts of these industrial processes.