H₂ production via dehydrogenation of formic acid (HCOOH, FA), sodium formate (HCOONa, SF), or their mixtures, at near-ambient conditions, T < 100 °C, P = 1 bar, is intensively pursued, in the context of the most economically and environmentally eligible technologies. Herein we discuss molecular catalysts (ML), consisting of a metal center (M, e.g., Ru, Ir, Fe, Co) and an appropriate ligand (L), which exemplify highly efficient Turnover Numbers (TONs) and Turnover Frequencies (TOFs) in H₂ production from FA/SF. Typically, many of these ML catalysts require the presence of a cofactor that promotes their optimal cycling. Thus, we distinguish the concept of such cofactors in additives vs. co-catalysts: When used at high concentrations, that is stoichiometric amounts vs. the substrate (HCOONa, SF), the cofactors are sacrificial additives. In contrast, co-catalysts are used at much lower concentrations, that is at stoichiometric amount vs. the catalyst. The first part of the present review article discusses the mechanistic key steps and key controversies in the literature, taking into account theoretical modeling data. Then, in the second part, the role of additives and co-catalysts as well as the role of the solvent and the eventual inhibitory role of H₂O are discussed in connection to the main mechanistic steps. For completeness, photons used as activators of ML catalysts are also discussed in the context of co-catalysts. In the third part, we discuss examples of promising hybrid nanocatalysts, consisting of a molecular catalyst ML attached on the surface of a nanoparticle. In the same context, we discuss nanoparticulate co-catalysts and hybrid co-catalysts, consisting of catalyst attached on the surface of a nanoparticle, and their role in the performance of molecular catalysts ML.

The development of low-carbon technologies that will facilitate the efficient use of hydrogen (H₂) as an energy carrier is a critical requirement of contemporary society. To this end, it is anticipated that the cost of H₂ production will become a key factor in tandem with production efficiency, process safety, and transport. Much effort has been made to create and develop new, reversible, and sustainable H₂ storage systems. Among current techniques, formic acid (FA) has been identified as an efficient energy carrier for H₂ storage. Numerous homogeneous catalysts based on transition metals with high activity and selectivity have been reported for selective FA dehydrogenation. In this review, we outline the recent advances in transition-metal molecular catalysts for FA dehydrogenation. Selected catalytic systems that could be implemented on an industrial scale and considered potential materials in fuel cell (FC) technology have been cost-evaluated. We highlight some critical engineering challenges faced during the technology’s scale-up process and explain other factors that are frequently ignored by academic researchers. Finally, we offer a critical assessment and identify several system limitations on an industrial scale that are currently impeding future implementation.

Oxidants are very active compounds that can cause damage to biological systems under specific environmental conditions. One effective way to counterbalance these adverse effects is the use of anti-oxidants. At low concentrations, an antioxidant is defined as a compound that can delay, control, or prevent an oxidative process. Antioxidants exist in plants, soil, and minerals; therefore, nature is a rich source of natural antioxidants, such as tocopherols and polyphenols. In nature, antioxidants perform in tandem with their bio-environment, which may tune their activity and protect them from degradation. In vitro use of antioxidants, i.e., out of their biomatrix, may encounter several drawbacks, such as auto-oxidation and polymerization. Artificial nanoantioxidants can be developed via surface modification of a nanoparticle with an antioxidant that can be either natural or synthetic, directly mimicking a natural antioxidant system. In this direction, state-of-the-art nanotechnology has been extensively incorporated to overcome inherent drawbacks encountered in vitro use of antioxidants, i.e., out of their biomatrix, and facilitate the production and use of antioxidants on a larger scale. Biomimetic nanoengineering has been adopted to optimize bio-medical antioxidant systems to improve stability, control release, enhance targeted administration, and overcome toxicity and biocompatibility issues. Focusing on biotechnological sciences, this review highlights the importance of nanoengineering in developing effective antioxidant structures and comparing the effectiveness of different nanoengineering methods. Additionally, this study gathers and clarifies the different antioxidant mechanisms reported in the literature and provides a clear picture of the existing evaluation methods, which can provide vital insights into bio-medical applications.