Facile synthesis of Bi2Se3/nitrogen-doped carbon dot nanoplates for aqueous zinc ion battery cathodes.

Bi2Se3 is a promising cathode material for aqueous zinc ion batteries (AZIBs), but its limited capacity and poor cycling stability deter its further use in the development of AZIBs. To solve this issue, Bi2Se3/NCD composites have been synthesized via a simple two-step solvothermal method. The introduction of nitrogen-doped carbon dots (NCDs) provides more active sites and makes the composite surface rich in functional groups, which facilitates contact with aqueous electrolytes. The results showed that Bi2Se3/NCDs improved the zinc storage properties of Bi2Se3 as a cathode material. The discharge specific capacity is 318 mA h g-1 at 0.1 A g-1. The cycling performance of Bi2Se3/NCDs was also relatively excellent compared to that of Bi2Se3. This work offers a productive and feasible strategy for metal chalcogenides (MCs) as cathode materials for AZIBs to improve the zinc storage capacity.

Ambient Ammonia Synthesis via Electrochemical Reduction of Nitrate Enabled by NiCo2 O4 Nanowire Array.

NiCo2 O4 nanowire array on carbon cloth (NiCo2 O4 /CC) is proposed as a highly active electrocatalyst for ambient nitrate (NO3 - ) reduction to ammonia (NH3 ). In 0.1 m NaOH solution with 0.1 m NaNO3 , such NiCo2 O4 /CC achieves a high Faradic efficiency of 99.0% and a large NH3 yield up to 973.2 µmol h-1  cm-2 . The superior catalytic activity of NiCo2 O4 comes from its half-metal feature and optimized adsorption energy due to the existence of Ni in the crystal structure. A Zn-NO3 - battery with NiCo2 O4 /CC cathode also shows a record-high battery performance.

Enhancing Electrocatalytic NO Reduction to NH3 by the CoS Nanosheet with Sulfur Vacancies.

Electrochemical reduction of NO to NH3 is of great significance for mitigating the accumulation of nitrogen oxides and producing valuable NH3. Here, we demonstrate that the CoS nanosheet with sulfur vacancies (CoS1-x) behaves as an efficient catalyst toward electrochemical NO-to-NH3 conversion. In 0.2 M Na2SO4 electrolyte, such CoS1-x displays a large NH3 yield rate (44.67 µmol cm-2 h-1) and a high Faradaic efficiency (53.62%) at -0.4 V versus the reversible hydrogen electrode, outperforming the CoS counterpart (27.02 µmol cm-2 h-1; 36.68%). Moreover, the Zn-NO battery with CoS1-x shows excellent performance with a power density of 2.06 mW cm-2 and a large NH3 yield rate of 1492.41 µg h-1 mgcat.-1. Density functional theory was performed to obtain mechanistic insights into the NO reduction over CoS1-x.

Amorphous Boron Carbide on Titanium Dioxide Nanobelt Arrays for High-Efficiency Electrocatalytic NO Reduction to NH3.

Electrocatalytic NO reduction is regarded as an attractive strategy to degrade the NO contaminant into useful NH3 , but the lack of efficient and stable electrocatalysts to facilitate such multiple proton-coupled electron-transfer processes impedes its applications. Here, we report on developing amorphous B2.6 C supported on a TiO2 nanoarray on a Ti plate (a-B2.6 C@TiO2 /Ti) as an NH3 -producing nanocatalyst with appreciable activity and durability toward the NO electroreduction. It shows a yield of 3678.6 µg h-1 cm-2 and a FE of 87.6 %, superior to TiO2 /Ti (563.5 µg h-1 cm-2 , 42.6 %) and a-B2.6 C/Ti (2499.2 µg h-1 cm-2 , 85.6 %). An a-B2.6 C@TiO2 /Ti-based Zn-NO battery achieves a power density of 1.7 mW cm-2 with an NH3 yield of 1125 µg h-1 cm-2 . An in-depth understanding of catalytic mechanisms is gained by theoretical calculations.

High-Performance Electrochemical NO Reduction into NH3 by MoS2 Nanosheet.

Electrochemical reduction of NO not only offers an attractive alternative to the Haber-Bosch process for ambient NH3 production but mitigates the human-caused unbalance of nitrogen cycle. Herein, we report that MoS2 nanosheet on graphite felt (MoS2 /GF) acts as an efficient and robust 3D electrocatalyst for NO-to-NH3 conversion. In acidic electrolyte, such MoS2 /GF attains a maximal Faradaic efficiency of 76.6 % and a large NH3 yield of up to 99.6 µmol cm-2 h-1 . Using MoS2 nanosheet-loaded carbon paper as the cathode, a proof-of-concept device of Zn-NO battery was assembled to deliver a discharge power density of 1.04 mW cm-2 and an NH3 yield of 411.8 µg h-1 mgcat. -1 . Calculations reveal that the positively charged Mo-edge sites facilitate NO adsorption/activation via an acceptance-donation mechanism and disfavor the binding of protons and the coupling of N-N bond.

Atomic-level modulation of electron density in iron sulfides for enhancing sodium storage kinetics.

Iron sulfides (FeS2) are promising anode materials for sodium ion batteries (SIBs); however, their inferior electronic conductivity, large volume swelling, and sluggish sodium ion diffusion kinetics lead to unsatisfactory rate performance and cycling durability. Heteroatom doping plays a crucial role in modifying the physicochemical properties of FeS2 anodes to enhance its sodium storage. Herein, ultra-fine Ni-doped FeS2 nanocrystals derived from a metal-organic framework (MOF) and in-situ anchored on a nitrogen doped carbon skeleton (Ni-FeS2@NC) are proposed to enhance both structural stability and reaction kinetics. Material characterization, electrochemical performance, and kinetics analysis demonstrate the critical role of Ni doping in sodium storage, particularly in accelerating Na+ diffusion efficiency. The N-doped carbon derived from the MOF can buffer the volume expansion and enhance the structural stability of electrode materials during sodiation/desodiation processes. As expected, Ni-FeS2@NC exhibits a high reversible capacity of 656.6 ± 65.1 mAh g-1 at 1.0 A g-1 after 200 cycles, superior rate performance (308.8 ± 6.0 mAh g-1 at 10.0 A g-1), and long-term cycling durability over 2000 cycles at 1.0 A g-1. Overall, this study presents an effective approach for enhancing the sodium storage performance and kinetics of anode materials for high efficiency SIBs.

TiO2-modified two-dimensional composite of nitrogen-doped molybdenum trioxide nanosheets as a high-performance anode for lithium-ion batteries.

Nitrogen-doped molybdenum trioxide (MoO3/NC) has drawbacks such as volume expansion during long-term charging and discharging cycles, which severely limit its further application. This work proposes the addition of titanium dioxide nanoparticles (TiO2 NPs) for performance improvement of MoO3/NC. TiO2 NPs embedded on the surface of a MoO3/NC nanosheet can alleviate its volume expansion and the accumulation of lithiated products and improve the conductivity of the electrode material. The results show that the MoO3/NC nanosheet decorated with TiO2 NPs (TiO2@MoO3/NC), when used as an electrode material, exhibited a discharge specific capacity of 419 mA h g-1 at a current density of 0.05 A g-1 and retained a discharge specific capacity of 517 mA h g-1 after 600 cycles at a current density of 1 A g-1.

Efficient Electrochemical Co-Reduction of Carbon Dioxide and Nitrate to Urea with High Faradaic Efficiency on Cobalt-Based Dual-Sites.

Renewable electricity-powered nitrate/carbon dioxide co-reduction reaction toward urea production paves an attractive alternative to industrial urea processes and offers a clean on-site approach to closing the global nitrogen cycle. However, its large-scale implantation is severely impeded by challenging C-N coupling and requires electrocatalysts with high activity/selectivity. Here, cobalt-nanoparticles anchored on carbon nanosheet (Co NPs@C) are proposed as a catalyst electrode to boost yield and Faradaic efficiency (FE) toward urea electrosynthesis with enhanced C-N coupling. Such Co NPs@C renders superb urea-producing activity with a high FE reaching 54.3% and a urea yield of 2217.5 µg h-1 mgcat. -1, much superior to the Co NPs and C nanosheet counterparts, and meanwhile shows strong stability. The Co NPs@C affords rich catalytically active sites, fast reactant diffusion, and sufficient catalytic surfaces-electrolyte contacts with favored charge and ion transfer efficiencies. The theoretical calculations reveal that the high-rate formation of *CO and *NH2 intermediates is crucial for facilitating urea synthesis.

Boosting electrochemical nitrate-to-ammonia conversion by self-supported MnCo2O4 nanowire array.

Direct electrocatalytic reduction of nitrate (NO3-) is an efficient route to simultaneously synthesize ammonia (NH3) and remove NO3- pollutants under ambient conditions, however, it is hindered by the lack of efficient and stable catalysts. Herein, a self-supported spinel-type MnCo2O4 nanowire array is demonstrated for exclusively catalyzing the conversion of NO3- to NH3, achieving a high Faradic efficiency of 97.1% and a large NH3 yield of 0.67 mmol h-1 cm-2. Furthermore, density functional analysis reveals that MnCo2O4 (220) surface has high activity for NO3- reduction with a low energy barrier of 0.46 eV for *NO to *NOH.

CoO nanoparticle decorated N-doped carbon nanotubes: a high-efficiency catalyst for nitrate reduction to ammonia.

Ambient electrochemical NO3- reduction is emerging as an appealing approach toward eliminating NO3- contaminants and generating NH3 simultaneously, but its efficiency is challenged by a lack of active and selective electrocatalysts. In this work, we report CoO nanoparticle decorated N-doped carbon nanotubes as an efficient catalyst for highly selective hydrogenation of NO3- to NH3. In 0.1 M NaOH electrolyte with 0.1 M NO3-, this catalyst is capable of achieving a large NH3 yield of up to 9041.6 ± 370.7 µg h-1 cm-2 and a high faradaic efficiency of 93.8 ± 1.5%, with excellent durability. Theoretical calculations reveal the catalytic mechanisms.

A 3D FeOOH nanotube array: an efficient catalyst for ammonia electrosynthesis by nitrite reduction.

Nitrite (NO2-) is a detrimental pollutant widely existing in groundwater sources, threatening public health. Electrocatalytic NO2- reduction settles the demand for removal of NO2- and is also promising for generating ammonia (NH3) at room temperature. A nanotube array directly grown on a current collector not only has a large surface area, but also exhibits improved structural stability and accelerated electron transport. Herein, a self-standing FeOOH nanotube array on carbon cloth (FeOOH NTA/CC) is proposed as a highly active electrocatalyst for NO2--to-NH3 conversion. As a 3D catalyst, the FeOOH NTA/CC is able to attain a surprising faradaic efficiency of 94.7% and a large NH3 yield of 11937 µg h-1 cm-2 in 0.1 M PBS (pH = 7.0) with 0.1 M NO2-. Furthermore, this catalyst also displays excellent durability in cyclic and long-term electrolysis tests.

Recent advances in MoS2-based materials for electrocatalysis.

The increasing energy demand and related environmental issues have drawn great attention worldwide, thus necessitating the development of sustainable technologies to preserve the ecosystems for future generations. Electrocatalysts for energy-conversion reactions such as the hydrogen evolution reaction (HER), nitrogen reduction reaction (NRR), and carbon dioxide reduction reaction (CO2RR) are at the heart of these renewable energy technologies, but they suffer from sluggish kinetics due to the multistep electron and mass transfer. State-of-the-art catalysts are thus highly desired to boost the conversion efficiencies, which are still inadequate. Recently, as a typical transition metal dichalcogenide, molybdenum disulfide (MoS2) with unique physicochemical properties has been verified as a promising material for catalyzing key electrochemical reactions (i.e., HER, NRR, and CO2RR), presenting excellent performances. Therefore, in this review, we give insight into the structure and synthetic strategies of MoS2. Recent advances in MoS2-based materials for the three key electrochemical reactions are briefly summarized. Open challenges and perspectives of MoS2-based electrocatalysts toward HER, NRR, and CO2RR are also outlined.

Cu nanoparticles decorated juncus-derived carbon for efficient electrocatalytic nitrite-to-ammonia conversion.

Electrocatalytic nitrite reduction to value-added NH3 can simultaneously achieve sustainable ammonia production and N-contaminant removal in natural environments, which has attracted widespread attention but still lacks efficient catalysts. In this work, Cu nanoparticles decorated juncus-derived carbon can be proposed as a high-active electrocatalyst for NO2--to-NH3 conversion, obtaining a high Faradaic efficiency of 93.2% and a satisfactory NH3 yield of 523.5 µmol h-1 mgcat.-1. Density functional theory calculations were applied to uncover insightful understanding of internal catalytic mechanism.

A TiO2-x nanobelt array with oxygen vacancies: an efficient electrocatalyst toward nitrite conversion to ammonia.

Electrocatalytic nitrite reduction not only holds significant potential in the control of nitrite contamination in the natural environment, but also is an attractive approach for sustainable ammonia synthesis. In this communication, we report that a TiO2-x nanobelt array with oxygen vacancies on a titanium plate is able to convert nitrite into ammonia with a high faradaic efficiency of 92.7% and a large yield of 7898 µg h-1 cm-2 in alkaline solution. This monolithic catalyst also shows high durability with the maintenance of its catalytic activity for 12 h. Theoretical calculations further reveal the critical role of oxygen vacancies in nitrite electroreduction.

High-efficiency NO electroreduction to NH3 over honeycomb carbon nanofiber at ambient conditions.

Electrocatalytic NO reduction is a promising technology for ambient NO removal with simultaneous production of highly value-added NH3. Herein, we report that honeycomb carbon nanofiber coated on carbon paper acts as an efficient metal-free catalyst for ambient electroreduction of NO to NH3. In 0.2 M Na2SO4 solution, such catalyst achieves an NH3 yield of 22.35 µmol h-1 cm-2 with a high Faradaic efficiency of up to 88.33%. Impressively, it also shows excellent stability for 10-h continuous electrolysis. Theoretical calculations reveal that the most active center of functional groups is -OH group for NO reduction with a low energy barrier (ΔG of 0.29 eV) for the potential-determining step (*NO + H → *HNO).

Co-NCNT nanohybrid as a highly active catalyst for the electroreduction of nitrate to ammonia.

Electrocatalytic nitrate (NO3-) reduction has emerged as an attractive dual-function strategy to produce ammonia (NH3) and simultaneously mitigate environmental issues. However, efficient electrocatalysts with high selectivity for NH3 synthesis are highly desired. In this work, we report the Co-NCNT nanohybrid as a highly active electrocatalyst towards NO3--to-NH3 conversion. In 0.1 M NaOH solution containing 0.1 M NO3-, the Co-NCNT catalyst is capable of attaining a large NH3 yield of 5996 µg h-1 cm-2 and a high faradaic efficiency of 92% at -0.6 V versus reversible hydrogen electrode. Moreover, it displays excellent electrochemical stability.

Co nanoparticle-decorated pomelo-peel-derived carbon enabled high-efficiency electrocatalytic nitrate reduction to ammonia.

Electrocatalytic nitrate reduction is a sustainable approach to produce ammonia and remediate water pollutant nitrate. Here, we show that Co nanoparticle-decorated pomelo-peel-derived carbon is an efficient electrocatalyst for nitrate reduction to ammonia with a faradaic efficiency of 90.1% and a yield of 1.1 mmol h-1 mgcat.-1.

A FeCo2O4 nanowire array enabled electrochemical nitrate conversion to ammonia.

Electrocatalytic nitrate (NO3-) reduction not only generates high-value ammonia (NH3) but holds significant potential in the control of NO3- contaminants in natural environments. Here, a bimetallic FeCo2O4 spinel nanowire array grown on carbon cloth is proposed as an efficient electrocatalyst for the conversion of NO3- to NH3 with a high faradaic efficiency of up to 95.9% and a large NH3 yield of 4988 µg h-1 cm-2. Furthermore, it also exhibits excellent stability during 16 h electrolysis.

N-doped carbon nanotubes supported CoSe2 nanoparticles: A highly efficient and stable catalyst for H2O2 electrosynthesis in acidic media.

Electrocatalytic oxygen reduction reaction (ORR) provides an attractive alternative to anthraquinone process for H2O2 synthesis. Rational design of earth-abundant electrocatalysts for H2O2 synthesis via a two-electron ORR process in acids is attractive but still very challenging. In this work, we report that nitrogen-doped carbon nanotubes as a multi-functional support for CoSe2 nanoparticles not only keep CoSe2 nanoparticles well dispersed but alter the crystal structure, which in turn improves the overall catalytic behaviors and thereby renders high O2-to-H2O2 conversion efficiency. In 0.1 M HClO4, such CoSe2@NCNTs hybrid delivers a high H2O2 selectivity of 93.2% and a large H2O2 yield rate of 172 ppm·h-1 with excellent durability up to 24 h. Moreover, CoSe2@NCNTs performs effectively for organic dye degradation via electro-Fenton process. Electronic Supplementary Material: Supplementary material (SEM images, EDX mapping images, XPS spectrum, XRD patterns, RRDE voltammogram, Tafel plots, cyclic voltammograms, UV-Vis spectra, and Tables S1) is available in the online version of this article at 10.1007/s12274-021-3474-0.

Reduced graphene oxide supported ZIF-67 derived CoP enables high-performance potassium ion storage.

Potassium-ion batteries (PIBs) are currently recognized as an emerging battery technology because of the rich resources and low cost of potassium. Nevertheless, investigations on exploiting suitable anode materials to meet stable potassium-ions storage remain to be a problem owing to the big radius size of potassium-ions. Herein, we designed N-doped carbon restricted CoP polyhedra embedded into reduced graphene oxide (rGO) sheet (CoP/NC@rGO) through coupling the function of ZIF-67 and rGO. For this composite, nano-scale CoP particles can be encapsulated by ZIF-67 derived carbon matrix, which significantly alleviates the volume change and promotes K+/e- transfer. Additionally, the combination of CoP/NC polyhedra and rGO nanosheets can build a fascinating 3D architecture to further improve the electronic conductivity of materials, as well as effectively preventing the aggregation of CoP/NC polyhedra. As a result, such composites can exhibit remarkable long-cycle performance, maintaining remarkable capacities of 177 mAh g-1 after 2800 cycles at 1 A g-1. This work provides a hopeful strategy that the combination of MOF-derived porous structures with rGO can effectively promote K+/e- transfer and improve the stability of electrode materials.