An official website of the United States government
Abstract The removal of carbon dioxide from the atmosphere by the marine biological pump is a key regulator of Earth’s climate; however, the ocean also serves as a large source of nitrous oxide, a potent greenhouse gas and ozone-depleting substance. Although biological carbon sequestration and nitrous oxide production have been individually studied in the ocean, their combined impacts on net greenhouse forcing remain uncertain. Here we show that the magnitude of nitrous oxide production in the epipelagic zone of the subtropical ocean covaries with remineralization processes and thus acts antagonistically to weaken the radiative benefit of carbon removal by the marine biological pump. Carbon and nitrogen isotope tracer incubation experiments and nitrogen isotope natural abundance data indicate enhanced biological activity promotes nitrogen recycling, leading to substantial nitrous oxide production via both oxidative and reductive pathways. These shallow-water nitrous oxide sources account for nearly half of the air–sea flux and counteract 6–27% (median 9%) of the greenhouse warming mitigation achieved by carbon export via the biological pump.
more »
« less
The impact of nitrogen oxides on electrochemical carbon dioxide reduction
Abstract The electroreduction of carbon dioxide offers a promising avenue to produce valuable fuels and chemicals using greenhouse gas carbon dioxide as the carbon feedstock. Because industrial carbon dioxide point sources often contain numerous contaminants, such as nitrogen oxides, understanding the potential impact of contaminants on carbon dioxide electrolysis is crucial for practical applications. Herein, we investigate the impact of various nitrogen oxides, including nitric oxide, nitrogen dioxide, and nitrous oxide, on carbon dioxide electroreduction on three model electrocatalysts (i.e., copper, silver, and tin). We demonstrate that the presence of nitrogen oxides (up to 0.83%) in the carbon dioxide feed leads to a considerable Faradaic efficiency loss in carbon dioxide electroreduction, which is caused by the preferential electroreduction of nitrogen oxides over carbon dioxide. The primary products of nitrogen oxides electroreduction include nitrous oxide, nitrogen, hydroxylamine, and ammonia. Despite the loss in Faradaic efficiency, the electrocatalysts exhibit similar carbon dioxide reduction performances once a pure carbon dioxide feed is restored, indicating a negligible long-term impact of nitrogen oxides on the catalytic properties of the model catalysts.
more »
« less
- Award ID(s):
- 1803200
- PAR ID:
- 10202061
- Publisher / Repository:
- Nature Publishing Group
- Date Published:
- Journal Name:
- Nature Communications
- Volume:
- 11
- Issue:
- 1
- ISSN:
- 2041-1723
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Improving the management of nitrogen fertilizer makes sense. It can reduce farm costs by increasing nitrogen use efficiency without reducing yields. It can also benefit our environment by reducing the emissions of a potent greenhouse gas called nitrous oxide. Better still, by improving nitrogen management, farmers can receive payment for reducing emissions of this gas through the market place. Agriculture is a source and a sink for greenhouse gases that affect our climate. All three of the major greenhouse gases are produced naturally in agricultural soils—carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). Nitrous oxide is the most important in all field crops but rice due to its link with the use of nitrogen fertilizer.more » « less
-
Electroreduction of carbon dioxide (CO2) or carbon monoxide (CO) toward C2+hydrocarbons such as ethylene, ethanol, acetate and propanol represents a promising approach toward carbon-negative electrosynthesis of chemicals. Fundamental understanding of the carbon─carbon (C-C) coupling mechanisms in these electrocatalytic processes is the key to the design and development of electrochemical systems at high energy and carbon conversion efficiencies. Here, we report the investigation of CO electreduction on single-atom copper (Cu) electrocatalysts. Atomically dispersed Cu is coordinated on a carbon nitride substrate to form high-density copper─nitrogen moieties. Chemisorption, electrocatalytic, and computational studies are combined to probe the catalytic mechanisms. Unlike the Langmuir-Hinshelwood mechanism known for copper metal surfaces, the confinement of CO adsorption on the single-copper-atom sites enables an Eley-Rideal type of C-C coupling between adsorbed (*CO) and gaseous [CO(g)] carbon moxide molecules. The isolated Cu sites also selectively stabilize the key reaction intermediates determining the bifurcation of reaction pathways toward different C2+products.more » « less
-
Abstract Electrochemical reduction of carbon dioxide (CO2RR) to value‐added products is a promising strategy to alleviate the greenhouse gas effect. Molecular catalysts, such as cobalt (II) phthalocyanine (CoPc), are known to be efficient electrocatalysts that are capable of converting CO2into carbon monoxide (CO). Herein, we report an axial modification strategy to enhance CoPc's CO2RR performance. After coordinating with axial ligands, the electron density of Co was depleted via π‐backbonding. This π‐backbonding weakened the Co‐CO bond, resulting in rapid desorption of CO. Also, the presence axial ligands elevated the Co dz2orbital energy, resulting in a significantly enhanced CO selectivity, evidenced by an increased faradaic efficiency (FE) from 82 % (CoPc) to 91 % and 94 % with the presence of pyridine (CoPc‐py) and imidizal ligands (CoPc‐im), respectively, at −0.82 V vs. RHE. Density functional theory calculations reveal that axial ligation of CoPc can reduce the energy barrier for CO2activation and facilitate the formation of*COOH.more » « less
-
Identifying new catalyst composition for carbon dioxide electroreduction to high-value products has been the center of attraction over the last several years. In this article, nickel selenide (NiSe 2 ) has been identified as a high-efficiency electrocatalyst for CO 2 electroreduction at neutral pH. Interestingly, NiSe 2 shows high selectivity towards specific reduction products, forming carbon-rich C2 products like ethanol and acetic acid exclusively at lower applied potential with 98.45% faradaic efficiency, while C1 products formic acid and carbon monoxide formed preferentially at higher applied potential. More importantly, the C2 products such as acetic acid and ethanol are obtained at very low applied potential, which further corroborates the novelty of this catalyst in CO 2 utilization with minimal energy expense. The NiSe 2 catalyst surface has been studied through density functional theory calculations which show that the adsorption energy of the CO intermediate on the NiSe 2 surface is optimal for extensive reduction through formation of C–C bonds but not strong enough for surface passivation, thus leading to high selectivity for C2 products. Such high efficiency of the catalyst can be a result of increased covalency of the selenide anion along with a high d-electron density of the Ni center. The hydrothermally synthesized NiSe 2 sample also shows high activity for oxygen evolution through electrocatalytic water splitting in alkaline medium, effectively making it a bifunctional catalyst which can lower the concentration of the atmospheric pollutant CO 2 while at the same time enriching the air with O 2 .more » « less
