Comparing Molecular Mechanisms in Solar NH3 Production and Relations with CO2 Reduction

Abstract

Molecular mechanisms for N2 fixation (solar NH3) and CO2 conversion to C2+ products in enzymatic conversion (nitrogenase), electrocatalysis, metal complexes and plasma catalysis are analyzed and compared. It is evidenced that differently from what is present in thermal and plasma catalysis, the electrocatalytic path requires not only the direct coordination and hydrogenation of undissociated N2 molecules, but it is necessary to realize features present in the nitrogenase mechanism. There is the need for (i) a multi-electron and -proton simultaneous transfer, not as sequential steps, (ii) forming bridging metal hydride species, (iii) generating intermediates stabilized by bridging multiple metal atoms and (iv) the capability of the same sites to be effective both in N2 fixation and in COx reduction to C2+ products. Only iron oxide/hydroxide stabilized at defective sites of nanocarbons was found to have these features. This comparison of the molecular mechanisms in solar NH3 production and CO2 reduction is proposed to be a source of inspiration to develop the next generation electrocatalysts to address the challenging transition to future sustainable energy and chemistry beyond fossil fuels.

Nanocarbon for Energy Material Applications: N2 Reduction Reaction

“…Although there are no definitive proofs, there is a general assumption in literature that the photo/electrocatalytic path involves an associative path. [69,81] In the associative path, a key question involves whether a sequential electron and proton transfers happens, or a concerted multielectron/proton transfer occurs as in the enzymatic path. The intermediates formed in one electron/proton transfer (as the first step in the associative path illustrated in Scheme 1, after N 2 coordination) are high energy molecules.…”

The Physical Chemistry and Chemical Physics (PCCP) Section of the International Journal of Molecular Sciences in Its Publications: The First 300 Thematic Articles in the First 3 Years

“…We assigned 18 articles to this thematic area, namely [ 128 , 235 , 236 , 237 , 238 , 239 , 240 , 241 , 242 , 243 , 244 , 245 , 246 , 247 , 248 , 249 , 250 , 251 ]. Their distribution within the typing specified in the Introduction is presented in Table 9 .…”

“…Taking this circumstance into account, two basic variants of their systematics are possible—by the nature of the transfer (energy transfer or charge transfer) and by the physicochemical nature of the material, in which such a transfer is carried out. In the variant of systematics by the nature of transfer, all articles presented in this Thematic Area can be divided into those in which studies are related to energy transfer, and those in which studies are related to charge transfer; the first include articles [ 128 , 236 , 237 , 238 , 239 , 241 , 242 , 246 , 247 , 249 ], the second, articles [ 235 , 240 , 243 , 244 , 245 , 248 , 250 , 251 ]. In the variant of systematics by the nature of the material, two types of articles can also be distinguished—those in which the energy/charge transfer is carried out in organic materials, namely [ 128 , 236 , 237 , 238 , 240 , 243 , 244 , 247 , 249 , 250 , 251 ], and those in which this transfer is carried out in inorganic materials [ 235 , 239 , 241 , 242 , 245 , 246 , 248 ].…”

“…In the variant of systematics by the nature of transfer, all articles presented in this Thematic Area can be divided into those in which studies are related to energy transfer, and those in which studies are related to charge transfer; the first include articles [ 128 , 236 , 237 , 238 , 239 , 241 , 242 , 246 , 247 , 249 ], the second, articles [ 235 , 240 , 243 , 244 , 245 , 248 , 250 , 251 ]. In the variant of systematics by the nature of the material, two types of articles can also be distinguished—those in which the energy/charge transfer is carried out in organic materials, namely [ 128 , 236 , 237 , 238 , 240 , 243 , 244 , 247 , 249 , 250 , 251 ], and those in which this transfer is carried out in inorganic materials [ 235 , 239 , 241 , 242 , 245 , 246 , 248 ]. The second variant of the systematics of articles seems to be more expedient, which we will use as the basis for further narration about Thematic Area 8.…”

“…In [ 236 ], the discussion was about the transfer of energy; an example of an article in which the study of charge transfer took place is [ 240 ], in which the intramolecular charge transfer in a probe based on benzothiazole was recorded. These two articles, as well as [ 128 , 244 , 251 ], were devoted to organic abiogenic materials; in other articles of the “organic” profile, namely [ 237 , 238 , 243 , 247 , 249 , 250 ], materials of biological origin, very diverse in terms of their physicochemical characteristics, were used as a medium for the transfer of energy/charge—polypeptides and their derivatives [ 237 , 243 , 250 ], nitrogenase [ 247 ], and various antibiotics [ 249 ]. Among the research articles related to the above processes in inorganic materials, it should be noted that [ 241 ] was devoted to the creation of quantum dots from carbon atoms in an array of tricarbon tetranitride C 3 N 4 , and article [ 246 ] demonstrated the expediency of short-term sonoporation using microbubbles encapsulated by nanoparticles elemental gold in the treatment of liver cancer before radiation therapy.…”