Insights into Nitrogenase Bioelectrocatalysis for Green Ammonia Production

Abstract

There is a growing interest in using ammonia as a liquid carrier of hydrogen for energy applications. Currently, ammonia is produced industrially by the Haber-Bosch process, which requires high temperature and high pressure. In contrast, bacteria have naturally evolved an enzyme known as nitrogenase, that is capable of producing ammonia and hydrogen at ambient temperature and pressure. Therefore, nitrogenases are attractive as a potentially more efficient means to produce ammonia via harnessing the unique properties of this enzyme. In recent years, exciting progress has been made in bioelectrocatalysis using nitrogenases to produce ammonia. Here, the prospects for developing biological ammonia production are outlined, key advances in bioelectrocatalysis by nitrogenases are highlighted, and possible solutions to the obstacles faced in realising this goal are discussed.

Green ammonia synthesis using CeO2/RuO2 nanolayers on vertical graphene catalyst via electrochemical route in alkaline electrolyte

“…Recently, the electrochemical production of ammonia has attracted immense attention and has become an intensely researched topic due to the diverse ever-increasing range of applications of ammonia including as fertilizers and industrial chemical commodities, which is also considered a renewable energy carrier and a carbon neutral liquid fuel. [1][2][3][4][5][6] Currently, ammonia is synthesized via the conventional high-pressure (<200 bar), high-temperature (400-500 °C)-driven process known as the "Haber-Bosch process". In addition, the ammonia synthesis reaction (N 2 + 3H 2 = 2NH 3 ) is an exothermic process (ΔH = −46 kJ mol −1 ) and thermodynamically favoured at low temperatures and high pressures.…”

Comparison between Fe2O3/C and Fe3C/Fe2O3/Fe/C Electrocatalysts for N2 Reduction in an Alkaline Electrolyte

“…For a sustainable low-/zero-emission energy future, green hydrogen is a versatile storage media for energy produced by intermittent renewables . In addition to the energy-intensive liquefaction or compression of hydrogen, cost-effective and sustainable methods for long-term storage and long-distance transportation of green hydrogen on a commercial scale should be developed. − One alternative option is to use ammonia (NH 3 ) as a renewable green hydrogen carrier. Currently, using the traditional Haber–Bosch process, more than 170 million tons of ammonia are produced (more than 96% of total ammonia production) and consumed annually worldwide.…”

Sustainable Biological Ammonia Production towards a Carbon-Free Society

“…In contrast to the Haber-Bosch process, which requires high temperature and pressure conditions, diazotrophic bacterial nitrogenases can produce ammonia at ambient temperature and pressure conditions [50]. Rhizobia, a type of diazotrophic bacteria, is a group of Gram-negative bacteria that includes Alphaproteobacteria and Betaproteobacteria [51,52].…”

“…Although the reaction rate of nitrogenases is slower than that of other enzymes, such as ribosomes and DNA polymerases, it is recognised as an excellent enzyme in that it can cleave the triple bond of nitrogen molecules at room temperature and normal pressure [56,57]. Therefore, to realise a carbon-free society, many studies have been conducted on nitrogenases from both basic and applied aspects [50,[58][59][60]. Numerous studies have elucidated the structure-activity relationship of nitrogenases [58,61,62].…”

“…Nitrogenases have the two following major problems: low stability and easy denaturation by oxygen, which should be solved [50]. Therefore, in a study to search for a highly stable nitrogenase, nitrogen fixation at 92 • C was detected using archaea isolated from hydrothermal vents in the deep sea [80].…”