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Reduction of oxides and oxoanions of carbon and nitrogen are of great contemporary importance as they are crucial for a sustainable environment. Substantial research has been dedicated to these areas in the last few decades. These reductions require both electrons and protons and their thermodynamic potentials often make them compete with hydrogen evolution reaction i.e., the reaction of protons and electrons to generate H2. These reactions are abundant in the environment in microorganisms and are facilitated by naturally occurring enzymes. This review brings together the state-of-the-art knowledge in the area of enzymatic reduction of CO2, NO2− and H+ with those of artificial molecular electrocatalysis. A simple ligand field theory-based design principle for electrocatalysts is first described. The electronic structure considerations developed automatically yield the basic geometry required and the 2nd sphere interactions which can potentially aid the activation and the further reduction of these small molecules. A systematic review of the enzymatic reaction followed by those reported in artificial molecular electrocatalysts is presented for the reduction of CO2, NO2− and H+. The review is focused on mechanism of action of these metalloenzymes and artificial electrocatalysts and discusses general principles that guide the rates and product selectivity of these reactions. The importance of the 2nd sphere interactions in both enzymatic and artificial molecular catalysis is discussed in detail. [ABSTRACT FROM AUTHOR]

A synthetic mimic of Fe–Fe hydrogenase (H2ase) is reported which bears a terminal alkyne group in the ligand. Using a terminal azide bearing organic linkers, this complex could be covalently attached to various electrode surfaces (e.g. edge plane graphite, reduced graphene oxide, etc.). The electrocatalytic hydrogen evolution (HER) efficiency of these constructs is investigated and the results show that the EPG–H2ase mimic construct is able to produce H2 from acidic water efficiently with over 90% selectivity. [ABSTRACT FROM AUTHOR]

To overcome the limitations of active edges, electrical conductivity and the surface area of MoS2 nanosheets, in the present work, we have successfully synthesized amorphous MoSx quantum dots with a larger number of edge atoms using a simple chemical reaction via a bottom-up approach. Structural and chemical characterizations are carried out by TEM, XRD, Raman and XPS measurements. XPS and EDX analyses indicate a larger number of unsaturated ‘S’ atoms in these ultrafine amorphous quantum dots. We have used this material as an efficient electrocatalyst for the hydrogen evolution reaction (HER) in neutral medium. The material shows a remarkably low overpotential (65 mV) towards HER compared to that of other crystalline MoS2 quantum dots or nanomaterials. The origin of such a low onset potential is the presence of more unsaturated sulfur (S22−) ligands and enhanced active edge sites. It also shows very high catalytic activity as well as good stability after 12 h of hydrogen generation in neutral water medium. [ABSTRACT FROM AUTHOR]

A synthetic mimic of Fe-Fe hydrogenase (H 2 ase) is reported which bears a terminal alkyne group in the ligand. Using a terminal azide bearing organic linkers, this complex could be covalently attached to various electrode surfaces (e.g. edge plane graphite, reduced graphene oxide, etc.). The electrocatalytic hydrogen evolution (HER) efficiency of these constructs is investigated and the results show that the EPG-H 2 ase mimic construct is able to produce H 2 from acidic water efficiently with over 90% selectivity.