Boron has been explored as p-block catalysts for nitrogen reduction reaction (NRR) by density functional theory. Unlike transition metals, on which the active centers need empty d orbitals to accept ...the lone-pair electrons of the nitrogen molecule, the sp3 hybrid orbital of the boron atom can form B-to-N π-back bonding. This results in the population of the N–N π* orbital and the concomitant decrease of the N–N bond order. We demonstrate that the catalytic activity of boron is highly correlated with the degree of charge transfer between the boron atom and the substrate. Among the 21 concept-catalysts, single boron atoms supported on graphene and substituted into h-MoS2 are identified as the most promising NRR catalysts, offering excellent energy efficiency and selectivity against hydrogen evolution reaction.
Ionic liquids are room-temperature molten salts, composed mostly of organic ions that may undergo almost unlimited structural variations. This review covers the newest aspects of ionic liquids in ...applications where their ion conductivity is exploited; as electrochemical solvents for metal/semiconductor electrodeposition, and as batteries and fuel cells where conventional media, organic solvents (in batteries) or water (in polymer-electrolyte-membrane fuel cells), fail. Biology and biomimetic processes in ionic liquids are also discussed. In these decidedly different materials, some enzymes show activity that is not exhibited in more traditional systems, creating huge potential for bioinspired catalysis and biofuel cells. Our goal in this review is to survey the recent key developments and issues within ionic-liquid research in these areas. As well as informing materials scientists, we hope to generate interest in the wider community and encourage others to make use of ionic liquids in tackling scientific challenges.
Electrochemical reduction of CO2 into liquid fuels is a promising approach to achieve a carbon‐neutral energy cycle. However, conventional electrocatalysts usually suffer from low energy efficiency ...and poor selectivity and stability. A 3D hierarchical structure composed of mesoporous SnO2 nanosheets on carbon cloth is proposed to efficiently and selectively electroreduce CO2 to formate in aqueous media. The electrode is fabricated by a facile combination of hydrothermal reaction and calcination. It exhibits an unprecedented partial current density of about 45 mA cm−2 at a moderate overpotential (0.88 V) with high faradaic efficiency (87±2 %), which is even larger than most gas diffusion electrodes. Additionally, the electrode also demonstrates flexibility and long‐term stability. The superior performance is attributed to the robust and highly porous hierarchical structure, which provides a large surface area and facilitates charge and mass transfer.
Mesoporous SnO2 nanosheets grown in situ on carbon cloth are used as a robust and flexible electrode for electroreducing CO2 to formate with high efficiency and selectivity. The superior performance is due to the hierarchical structure, which provides high surface area, fast charge and mass transport, and robustness. This electrode shows promise for practical artificial photosynthesis devices.
Ammonia (NH3) is one of the most widely produced chemicals worldwide. It has application in the production of many important chemicals, particularly fertilizers. It is also, potentially, an important ...energy storage intermediate and clean energy carrier. Ammonia production, however, mostly uses fossil fuels and currently accounts for more than 1.6% of global CO2 emissions (0.57 Gt in 2015). Here we describe a solar-driven nanostructured photoelectrochemical cell based on plasmon-enhanced black silicon for the conversion of atmospheric N2 to ammonia producing yields of 13.3 mg m(-2) h(-1) under 2 suns illumination. The yield increases with pressure; the highest observed in this work was 60 mg m(-2) h(-1) at 7 atm. In the presence of sulfite as a reactant, the process also offers a direct solar energy route to ammonium sulfate, a fertilizer of economic importance. Although the yields are currently not sufficient for practical application, there is much scope for improvement in the active materials in this cell.
Two‐dimensional (2D) materials are known to be useful in catalysis. Engineering 3D bulk materials into the 2D form can enhance the exposure of the active edge sites, which are believed to be the ...origin of the high catalytic activity. Reported herein is the production of 2D “few‐layer” antimony (Sb) nanosheets by cathodic exfoliation. Application of this 2D engineering method turns Sb, an inactive material for CO2 reduction in its bulk form, into an active 2D electrocatalyst for reduction of CO2 to formate with high efficiency. The high activity is attributed to the exposure of a large number of catalytically active edge sites. Moreover, this cathodic exfoliation process can be coupled with the anodic exfoliation of graphite in a single‐compartment cell for in situ production of a few‐layer Sb nanosheets and graphene composite. The observed increased activity of this composite is attributed to the strong electronic interaction between graphene and Sb.
Less is more: By engineering bulk antimony using an electrochemical exfoliation method, two‐dimensional antimony nanosheets and their composite with graphene were formed. The electrocatalytic activity of these two materials towards reducing CO2 to formate were evaluated, thus showing that the materials were more active than bulk antimony.
Based on the structure of the nitrogenase FeMo cofactor (FeMoco), it is reported that Fe deposited on MoS2 2D sheets exhibits high selectivity towards the spontaneous fixation of N2 against ...chemisorption of CO2 and H2O. DFT predictions also indicate the ability of this material to convert N2 into NH3 with a maximum energy input of 1.02 eV as an activation barrier for the first proton–electron pair transfer.
Bosch–Haber alternative? Mild conditions for N2 capture and catalytic conversion into NH3 is a key priority for “green fuels” technology. DFT findings show that Fe deposited on MoS2 2D sheets selectively captures N2 gas and converts N2 into NH3 with a maximum energy input of 1.02 eV, which arises from the activation barrier for the first H+/e− pair transfer.
Shuttling protons in ammonia synthesis
An electrochemical route to ammonia could substantially lower the greenhouse gas emissions associated with the current thermal Haber-Bosch process. One ...relatively promising option under study involves reductive formation of lithium nitride, which can be protonated to ammonia. However, the ethanol used to date as a local proton source in these studies may degrade under the reaction conditions. Suryanto
et al.
report the use of a tetraalkyl phosphonium salt in place of ethanol (see the Perspective by Westhead
et al.
). This cation can stably undergo deprotonation–reprotonation cycles and, as an added benefit, it enhances the ionic conductivity of the medium.
Science
, abg2371, this issue p.
1187
; see also abi8329, p.
1149
A phosphonium cation acts as a stable proton shuttle during electrochemical ammonia synthesis.
Ammonia (NH
3
) is a globally important commodity for fertilizer production, but its synthesis by the Haber-Bosch process causes substantial emissions of carbon dioxide. Alternative, zero-carbon emission NH
3
synthesis methods being explored include the promising electrochemical lithium-mediated nitrogen reduction reaction, which has nonetheless required sacrificial sources of protons. In this study, a phosphonium salt is introduced as a proton shuttle to help resolve this limitation. The salt also provides additional ionic conductivity, enabling high NH
3
production rates of 53 ± 1 nanomoles per second per square centimeter at 69 ± 1% faradaic efficiency in 20-hour experiments under 0.5-bar hydrogen and 19.5-bar nitrogen. Continuous operation for more than 3 days is demonstrated.
PDF
