Hydrogen fuel is considered as the cleanest renewable resource and the primary alternative to fossil fuels for future energy supply. Sustainable hydrogen generation is the major prerequisite to realize future hydrogen economy. The electrocatalytic hydrogen evolution reaction (HER), as the vital step of water electrolysis to H2 production, has been the subject of extensive study over the past decades. In this comprehensive review, we first summarize the fundamentals of HER and review the recent state-of-the-art advances in the low-cost and high-performance catalysts based on noble and non-noble metals, as well as metal-free HER electrocatalysts. We systemically discuss the insights into the relationship among the catalytic activity, morphology, structure, composition, and synthetic method. Strategies for developing an effective catalyst, including increasing the intrinsic activity of active sites and/or increasing the number of active sites, are summarized and highlighted. Finally, the challenges, perspectives, and research directions of HER electrocatalysis are featured.

Recent Advances in Electrocatalytic Hydrogen Evolution Using Nanoparticles.

Improving the knowledge of the relationship between structure and properties is fundamental in catalysis. Recently, researchers have developed a variety of well-controlled methods to synthesize atomically precise metal nanoclusters (NCs). NCs have shown high catalytic activity and unique selectivity in many catalytic reactions, which are related to their ultrasmall size, abundant unsaturated active sites, and unique electronic structure different from that of traditional nanoparticles (NPs). More importantly, because of their definite structure and monodispersity, they are used as model catalysts to reveal the correlation between catalyst performance and structure at the atomic scale. Therefore, this review aims to summarize the recent progress on NCs in catalysis and provide potential theoretical guidance for the rational design of high-performance catalysts. First a brief summary of the synthetic strategies and characterization methods of NCs is provided. Then the primary focus of this review—the model ...

Atomically Precise Noble Metal Nanoclusters as Efficient Catalysts: A Bridge between Structure and Properties.

Redox catalysis, including photocatalysis and (photo)electrocatalysis, may alleviate global warming and energy crises by removing excess CO2 from the atmosphere and converting it to value-added resources. Nano-to-atomic two-dimensional (2D) materials, clusters and single atoms are superior catalysts because of their engineerable ultrathin/small dimensions and large surface areas and have attracted worldwide research interest. Given the current gap between research and applications in CO2 reduction, our review systematically and constructively discusses nano-to-atomic surface strategies for catalysts reported to date. This work is expected to drive and benefit future research to rationally design surface strategies with multi-parameter synergistic impacts on the selectivity, activity and stability of next-generation CO2 reduction catalysts, thus opening new avenues for sustainable solutions to climate change, energy and environmental issues, and the potential industrial economy.

Surface strategies for catalytic CO2 reduction: from two-dimensional materials to nanoclusters to single atoms

Having access to clean water is a mandatory requirement for the proper development of living beings So, addressing the removal of contaminants from aquatic systems should be a priority research topic in order to restore ecosystem balance and secure a more sustainable future The fascinating structures and striking physical properties of metal–organic frameworks (MOFs) have revealed them as excellent platforms for the removal of harmful species from water In this review, we have focused our attention on critically highlighting the latest developments achieved in the adsorptive removal of inorganic – metal cations, inorganic acids, oxyanions/cations, nuclear wastes and other inorganic anions – and organic – pharmaceuticals and personal care products, artificial sweeteners and feed additives, agricultural products, organic dyes and industrial products – contaminants commonly found in wastewater using MOF technologies In particular, we have attempted to give a clear insight into the different synthetic strategies for water remediation, stressing the wide tunability of MOFs For this purpose, we have classified these two kinds of pollutants into different subfamilies, based on their chemical composition or common use Finally, we have proposed some future trends and challenges that need to be addressed for widening the range of applicability of MOFs and making solid headway towards sustainable development

Metal–organic framework technologies for water remediation: towards a sustainable ecosystem

N-Heterocyclic carbenes (NHC) are nowadays ubiquitous and indispensable in many research fields, and it is not possible to imagine modern transition metal and main group element chemistry without t...

N-Heterocyclic Carbene Adducts of Main Group Elements and Their Use as Ligands in Transition Metal Chemistry.

High-temperature ferromagnetic materials with planar surfaces are promising candidates for spintronics applications. Using state-of-the-art density functional theory (DFT) calculations, transition metal (TM = Cr, Mn, and Fe) incorporated graphitic carbon nitride (TM@gt-C3N4) systems are investigated as possible spintronics devices. Interestingly, ferromagnetism and half-metallicity were observed in all of the TM@gt-C3N4 systems. We find that Cr@gt-C3N4 is a nearly half-metallic ferromagnetic material with a Curie temperature of ∼450 K. The calculated Curie temperature is noticeably higher than other planar 2D materials studied to date. Furthermore, it has a steel-like mechanical stability and also possesses remarkable dynamic and thermal (500 K) stability. The calculated magnetic anisotropy energy (MAE) in Cr@gt-C3N4 is as high as 137.26 μeV per Cr. Thereby, such material with a high Curie temperature can be operated at high temperatures for spintronics devices.

Transition-metal embedded carbon nitride monolayers: high-temperature ferromagnetism and half-metallicity.

Thermochemical and electrochemical CO2 reduction on octahedral Cu nanocluster: Role of solvent towards product selectivity

Organomercurials including methylmercury are ubiquitous environmental pollutants and highly toxic to humans. Now it could be shown that N-methylimidazole based thiones/selones having an N-CH2CH2OH substituent are remarkably effective in detoxifying various organomercurials to produce less toxic HgE (E=S, Se) nanoparticles. Compounds lacking the N-CH2CH2OH substituent failed to produce HgE nanoparticles upon treatment with organomercurials, suggesting that this moiety plays a crucial role in the detoxification by facilitating the desulfurization and deselenization processes. This novel way of detoxifying organomercurials may lead to the discovery of new compounds to treat patients suffering from methylmercury poisoning.

Chemical Detoxification of Organomercurials.

We have carried out computational studies on the CO2 hydrogenation reaction catalyzed by three different Mn-based complexes (Mn1, Mn2, and Mn3) to understand the role of σ-donor (PMe3) and π-acceptor (CO) character of the ligands. Further, the role of a different set of σ-donor and π-acceptor ligands is studied as the studied CO (π-acceptor and PMe3 (σ-donor) ligands have the differences not only in electronic properties but also in steric effects. Here, we find that the σ-donor ligands (PMe3/PH3) favor the hydride transfer, whereas the π-acceptor ligands (CO/PF3) favor the heterolytic H2-cleavege. The energy profile diagram shows that the hydride transfer is the rate-determining step when the CO2 hydrogenation reaction is catalyzed by a Mn-complex containing σ-donor (PMe3/PH3) and π-acceptor (CO/PF3) ligands.

Catalytic Hydrogenation of CO2 by Manganese Complexes: Role of π-Acceptor Ligands

A bifunctional, chelating N-heterocyclic carbene-pyridine (NHC-pyridine) containing Mn(I) complex [MnBr(NHC-pyridine)(CO)3] displays a strong selectivity for CO2 reduction over proton reduction. Interestingly, the two-electron reduction of this complex occurs at a single potential, as opposed to MnBr(bpy)(CO)3, which is reduced by two electrons in two separate one-electron reductions. Here, the Gibbs free energy barriers, reduction potentials, rate constants, and pKa values are predicted with theory to understand the one- vs two-electron reduction mechanism. The effects of weak and strong Bronsted acids [HCl, TFE (2,2,2-trifluoroethanol), PhOH, CH3OH, and H2O] are studied to gauge the preference for CO2 vs proton reduction; water is found to be an ideal proton donor that allows for strong CO2 selectivity.

Kuber Singh Rawat

Papers

Transition-metal embedded carbon nitride monolayers: high-temperature ferromagnetism and half-metallicity.

Thermochemical and electrochemical CO2 reduction on octahedral Cu nanocluster: Role of solvent towards product selectivity

Chemical Detoxification of Organomercurials.

Catalytic Hydrogenation of CO2 by Manganese Complexes: Role of π-Acceptor Ligands

N-Heterocylic Carbene-Based Mn Electrocatalyst for Two-Electron CO2 Reduction over Proton Reduction