The development of electrocatalysts capable of efficient reduction of nitrate (NO3−) to ammonia (NH3) is drawing increasing interest for the sake of low carbon emission and environmental protection. Herein, we present a CuCo bimetallic catalyst able to imitate the bifunctional nature of copper-type nitrite reductase, which could easily remove NO2− via the collaboration of two active centers. Indeed, Co acts as an electron/proton donating center, while Cu facilitates NOx− adsorption/association. The bio-inspired CuCo nanosheet electrocatalyst delivers a 100 ± 1% Faradaic efficiency at an ampere-level current density of 1035 mA cm−2 at −0.2 V vs. Reversible Hydrogen Electrode. The NH3 production rate reaches a high activity of 4.8 mmol cm−2 h−1 (960 mmol gcat−1 h−1). A mechanistic study, using electrochemical in situ Fourier transform infrared spectroscopy and shell-isolated nanoparticle enhanced Raman spectroscopy, reveals a strong synergy between Cu and Co, with Co sites promoting the hydrogenation of NO3− to NH3 via adsorbed *H species. The well-modulated coverage of adsorbed *H and *NO3 led simultaneously to high NH3 selectivity and yield.

We report a facile and low-cost bottom-up synthesis of ultrathin Zn(bim)(OAc) MOF nanosheets (with thicknesses of ∼5 nm and a high yield of ∼65%) and their derived N-doped porous ultrathin (2.5 ± 0.8 nm) carbon nanosheets (UT-CNSs) for energy storage.

Although the planar square Fe-N 4 is considered to be the basic unit of the active Fe-N 4 -based moieties, the exact local structure of such moieties has not yet been determined due to that the axial ligands and the second coordination sphere (i.e., the surrounding carbon matrix) of Fe-N 4 are unclear. [8] Based on the computational hydrogen electrode (CHE) model, the theoretical ORR onset potentials of Fe-N 4 in different models were as low as 0.25-0.43 V versus RHE (V RHE ), [9,10] much lower than the experimentally measured ones on Fe-N-C (0.82-0.95 V RHE ). Besides, some new active moieties in Fe-N-C (e.g., FeON 4 , Fe(OH)N 4 , and FeN 4 Cl) were proposed by using in situ characterizations or CHE modeling, [11][12][13][14] revealing that the axialligand coordination played a critical role in high-activity Fe-N 4 -based moieties. However, these studies were carried out on Fe-N-C that contained not only the Fe-N 4 sites but also a large number of other ORR active sites (such as the N-doped carbon and intrinsic defects of carbon), in which the implemented modifications would affect the ORR activities of different active sites and sometimes even alter the structure of the carbon matrix. [15] That is, the observed ORR activity improvement of the Fe-N-C after such modifications could not be solely attributed to the enhancement of the intrinsic ORR activity of Fe-N 4 and thus the mechanism associated with the improvement is still ambiguous. To this end, developing a model catalyst as a studying platform is highly demanded to reveal the regulation mechanism of axial-ligand coordination on the catalytic activity of Fe-N 4 sites.Iron porphyrin (FePr) and iron phthalocyanine (FePc) are widely used molecular model catalysts with Fe-N 4 as the only kind of ORR active sites. [16] Although some modified FePc and FePr with axially coordinated Fe-N 4 moieties have been reported in recent papers, [17][18][19] only a few strong ligands (e.g., CN − and pyridine) could perform such axial coordination due to that the FePc and FePr are more inclined to exist as the D4h symmetry structure with highly concentrated local electrons. [17] In order to systematically study the correlation between the axial ligands and the catalytic activity of Fe-N 4 sites, it is necessary to explore a Fe-N 4 -based molecular model catalyst with a stronger axial coordination ability. Poly(phthalocyanine iron) (PFePc) is an alkali-soluble Identifying the actual structure and tuning the catalytic activity of Fe-N 4based moieties, well-recognized high-activity sites in the oxygen reduction reaction (ORR) are challenging problems. Herein, by using poly(iron phthalocyanine) (PFePc) as an Fe-N 4 -based model electrocatalyst, a mechanistic insight into the effect of axial ligands on the ORR catalytic activity of Fe-N 4 is provided and it is revealed that the ORR activity of Fe-N 4 sites with OH desorption as a rate-determining step is related to the energy level gap between the OH p x p y and Fe 3d z 2 , which can be tuned by regulating the field strength of the...

No abstract

The recent progress on the fabrication of two-dimensional metal–organic frameworks and their derivatives as well as their applications in electrochemical energy storage and electrocatalysis are reviewed.

The incorporation of oxygen vacancies in anatase TiO has been studied as a promising way to accelerate the transport of electrons and Na ions, which is important for achieving excellent electrochemical properties for anatase TiO. However, wittingly introducing oxygen vacancies in anatase TiO for sodium-ion anodes by a facile and effective method is still a challenge. In this work, we report an innovative method to introduce oxygen vacancies into the urchin-like N-doped carbon coated anatase TiO (NC-DTO) by a facile plasma treatment. The superiorities of the oxygen vacancies combined with the conductive N-doped carbon coating enable the obtained NC-DTO of greatly improved sodium storage performance. When served as the anode for sodium-ion batteries, the NC-DTO electrode shows superior electrochemical performance (capacity: 272 mA h g at 0.25 C, capacity retention: 98.8% after 5000 cycles at 10 C, as well as ultrahigh capacity: 150 mA h g at 15 C). Density functional theory calculations combined with experimental results suggest that considerably improved sodium storage performance of NC-DTO is due to the enhanced electronic conductivity from the N-doped carbon layer as well as narrowed band gap and lowered sodiation energy barrier from the introduction of oxygen vacancies. This work highlights that introducing oxygen vacancies into TiO by plasma is a promising method to enhance the electrochemical property of TiO, which also can be applied to different metal oxides for energy storage devices.

No abstract

No abstract