Bioelectrochemical Haber–Bosch Process: An Ammonia‐Producing H₂/N₂ Fuel Cell

Abstract

Nitrogenases are the only enzymes known to reduce molecular nitrogen (N2) to ammonia (NH3). By using methyl viologen (N,N′‐dimethyl‐4,4′‐bipyridinium) to shuttle electrons to nitrogenase, N2 reduction to NH3 can be mediated at an electrode surface. The coupling of this nitrogenase cathode with a bioanode that utilizes the enzyme hydrogenase to oxidize molecular hydrogen (H2) results in an enzymatic fuel cell (EFC) that is able to produce NH3 from H2 and N2 while simultaneously producing an electrical current. To demonstrate this, a charge of 60 mC was passed across H2 /N2 EFCs, which resulted in the formation of 286 nmol NH3 mg−1 MoFe protein, corresponding to a Faradaic efficiency of 26.4 %.

Efficient Electrocatalytic N2 Fixation with MXene under Ambient Conditions

“…7 As an alternative technology, electrochemical conversion can be carried out under ambient conditions as a natural process of microorganisms with nitrogenase enzymes that synthesize NH 3 from H 2 O, electrons, and atmospheric N 2 . 8,9 To date, several efforts (including our recent work) have been devoted to optimizing electrocatalytic centers to obtain acceptable NRR activity; [10][11][12][13][14][15][16] the extremely sluggish reaction kinetics and ultralow selectivity (current efficiency of less than 1%) of most catalysts associated with electrochemical NRR under ambient conditions still pose a significant challenge for ideal catalyst design. [17][18][19] Two-dimensional (2D) MXene has been extensively studied for use in membrane separation, lithium batteries, photocatalysis, and electrocatalysis.…”

Highly Selective Electrochemical Reduction of Dinitrogen to Ammonia at Ambient Temperature and Pressure over Iron Oxide Catalysts

“…[5,6] Another challenge is the kinetically complex dinitrogen (N 2 )r eductionp rocess, which involves multiple electron transfers and complex intermediates. [8,9] Accordingly, alternative approaches to ammonia synthesis under more benign conditions are attractive in terms of as ustainable and decentralized ammonia industry.C ertain bacteria are able to convert N 2 into NH 3 with the use of the nitrogenase enzyme under mild conditions;t his has motivated researchers to explore various strategies for artificial nitrogen fixation, which include homogeneous catalysis on metal-dinitrogen complexes, [10,11] photocatalytic routes on semiconductors, [12] bioelectrochemical methods, [13] ande lectrochemical methods. The current Haber-Bosch process also requires ac ontinuous supplyo fu ltrapure hydrogen, which is almoste xclusively produced from fossil fuels, leads to as ubstantial amount of CO 2 emissions, and requires highly centralized distributions.…”

“…The current Haber-Bosch process also requires ac ontinuous supplyo fu ltrapure hydrogen, which is almoste xclusively produced from fossil fuels, leads to as ubstantial amount of CO 2 emissions, and requires highly centralized distributions. [8,9] Accordingly, alternative approaches to ammonia synthesis under more benign conditions are attractive in terms of as ustainable and decentralized ammonia industry.C ertain bacteria are able to convert N 2 into NH 3 with the use of the nitrogenase enzyme under mild conditions;t his has motivated researchers to explore various strategies for artificial nitrogen fixation, which include homogeneous catalysis on metal-dinitrogen complexes, [10,11] photocatalytic routes on semiconductors, [12] bioelectrochemical methods, [13] ande lectrochemical methods. [14] Amongt hese, the electrochemical approach has provedp articularly promising because it can be powered from renewable energy sourcesa nd has the potential to reduce energy input, simplify reactor design, and increase economic viability,w hich allows for small-scale, low-costd evices that would be applic <able in remote areas.…”

Looking for Options to Sustainably Fixate Nitrogen. Are Molecular Metal Oxides Catalysts a Viable Avenue?

“…The detailed explanation for the necessary loss of a cell’s energy currency (ATP) associated with nitrogenase activity remains elusive ( Rabo and Schoonover, 2001 ; Milton et al, 2017 ) but it is assumed to be essential to reduce the activation barriers associated to the catalysis of the intermediates that lead to the overall reaction ( Van Der Ham et al, 2014 ) and to activate the transfer of electrons ( Rutledge and Tezcan, 2020 ). Also, the electron transfer to the substrate in nitrogenase seems to follow the description drawn in 1978 by Thorneley and colleagues ( Thorneley et al, 1978 ), but the delicate and precise donation of electrons, protons and energy is not fully deciphered yet.…”