Synthesis of Hydroxylamine via Ketone-Mediated Nitrate Electroreduction.

Hydroxylamine (HA, NH2OH) is a critical feedstock in the production of various chemicals and materials, and its efficient and sustainable synthesis is of great importance. Electroreduction of nitrate on Cu-based catalysts has emerged as a promising approach for green ammonia (NH3) production, but the electrosynthesis of HA remains challenging due to overreduction of HA to NH3. Herein, we report the first work on ketone-mediated HA synthesis using nitrate in water. A metal-organic-framework-derived Cu catalyst was developed to catalyze the reaction. Cyclopentanone (CP) was used to capture HA in situ to form CP oxime (CP-O) with C═N bonds, which is prone to hydrolysis. HA could be released easily after electrolysis, and CP was regenerated. It was demonstrated that CP-O could be formed with an excellent Faradaic efficiency of 47.8%, a corresponding formation rate of 34.9 mg h-1 cm-2, and a remarkable carbon selectivity of >99.9%. The hydrolysis of CP-O to release HA and CP regeneration was also optimized, resulting in 96.1 mmol L-1 of HA stabilized in the solution, which was significantly higher than direct nitrate reduction. Detailed in situ characterizations, control experiments, and theoretical calculations revealed the catalyst surface reconstruction and reaction mechanism, which showed that the coexistence of Cu0 and Cu+ facilitated the protonation and reduction of *NO2 and *NH2OH desorption, leading to the enhancement for HA production.

Improving CO2-to-C2+ Product Electroreduction Efficiency via Atomic Lanthanide Dopant-Induced Tensile-Strained CuOx Catalysts.

Cu is a promising electrocatalyst in CO2 reduction reaction (CO2RR) to high-value C2+ products. However, as important C-C coupling active sites, the Cu+ species is usually unstable under reduction conditions. How atomic dopants affect the performance of Cu-based catalysts is interesting to be studied. Herein, we first calculated the difference between the thermodynamic limiting potentials of CO2RR and the hydrogen evolution reaction, as well as the *CO binding energy over Cu2O doped with different metals, and the results indicated that doping atomic Gd into Cu2O could improve the performance of the catalyst effectively. On the basis of the theoretical study, we designed Gd1/CuOx catalysts. The distinctive electronic structure and large ion radii of Gd not only keep the Cu+ species stable during the reaction but also induce tensile strain in Gd1/CuOx, resulting in excellent performance of the catalysts for electroreduction of CO2 to C2+ products. The Faradic efficiency of C2+ products could reach 81.4% with a C2+ product partial current density of 444.3 mA cm-2 at -0.8 V vs a reversible hydrogen electrode. Detailed experimental and theoretical studies revealed that Gd doping enhanced CO2 activation on the catalyst, stabilized the key intermediate O*CCO, and reduced the energy barrier of the C-C coupling reaction.

Oxophilicity-Controlled CO2 Electroreduction to C2+ Alcohols over Lewis Acid Metal-Doped Cuδ+ Catalysts.

Cu-based electrocatalysts have great potential for facilitating CO2 reduction to produce energy-intensive fuels and chemicals. However, it remains challenging to obtain high product selectivity due to the inevitable strong competition among various pathways. Here, we propose a strategy to regulate the adsorption of oxygen-associated active species on Cu by introducing an oxophilic metal, which can effectively improve the selectivity of C2+ alcohols. Theoretical calculations manifested that doping of Lewis acid metal Al into Cu can affect the C-O bond and Cu-C bond breaking toward the selectively determining intermediate (shared by ethanol and ethylene), thus prioritizing the ethanol pathway. Experimentally, the Al-doped Cu catalyst exhibited an outstanding C2+ Faradaic efficiency (FE) of 84.5% with remarkable stability. In particular, the C2+ alcohol FE could reach 55.2% with a partial current density of 354.2 mA cm-2 and a formation rate of 1066.8 µmol cm-2 h-1. A detailed experimental study revealed that Al doping improved the adsorption strength of active oxygen species on the Cu surface and stabilized the key intermediate *OC2H5, leading to high selectivity toward ethanol. Further investigation showed that this strategy could also be extended to other Lewis acid metals.

High-Rate CO2 Electrolysis to Formic Acid over a Wide Potential Window: An Electrocatalyst Comprised of Indium Nanoparticles on Chitosan-Derived Graphene.

Realizing industrial-scale production of HCOOH from the CO2 reduction reaction (CO2 RR) is very important, but the current density as well as the electrochemical potential window are still limited to date. Herein, we achieved this by integration of chemical adsorption and electrocatalytic capabilities for the CO2 RR via anchoring In nanoparticles (NPs) on biomass-derived substrates to create In/X-C (X=N, P, B) bifunctional active centers. The In NPs/chitosan-derived N-doped defective graphene (In/N-dG) catalyst had outstanding performance for the CO2 RR with a nearly 100 % Faradaic efficiency (FE) of HCOOH across a wide potential window. Particularly, at 1.2 A ⋅ cm-2 high current density, the FE of HCOOH was as high as 96.0 %, and the reduction potential was as low as -1.17 V vs RHE. When using a membrane electrode assembly (MEA), a pure HCOOH solution could be obtained at the cathode without further separation and purification. The FE of HCOOH was still up to 93.3 % at 0.52 A ⋅ cm-2 , and the HCOOH production rate could reach 9.051 mmol ⋅ h-1 ⋅ cm-2 . Our results suggested that the defects and multilayer structure in In/N-dG could not only enhance CO2 chemical adsorption capability, but also trigger the formation of an electron-rich catalytic environment around In sites to promote the generation of HCOOH.

Boosting Electrocatalytic Nitrate-to-Ammonia via Tuning of N-Intermediate Adsorption on a Zn-Cu Catalyst.

The renewable-energy-powered electroreduction of nitrate (NO3 - ) to ammonia (NH3 ) has garnered significant interest as an eco-friendly and promising substitute for the Haber-Bosch process. However, the sluggish kinetics hinders its application at a large scale. Herein, we first calculated the N-containing species (*NO3 and *NO2 ) binding energy and the free energy of the hydrogen evolution reaction over Cu with different metal dopants, and it was shown that Zn was a promising candidate. Based on the theoretical study, we designed and synthesized Zn-doped Cu nanosheets, and the as-prepared catalysts demonstrated excellent performance in NO3 - -to-NH3 . The maximum Faradaic efficiency (FE) of NH3 could reach 98.4 % with an outstanding yield rate of 5.8 mol g-1 h-1 , which is among the best results up to date. The catalyst also had excellent cycling stability. Meanwhile, it also presented a FE exceeding 90 % across a wide potential range and NO3 - concentration range. Detailed experimental and theoretical studies revealed that the Zn doping could modulate intermediates adsorption strength, enhance NO2 - conversion, change the *NO adsorption configuration to a bridge adsorption, and decrease the energy barrier, leading to the excellent catalytic performance for NO3 - -to-NH3 .

In Situ Periodic Regeneration of Catalyst during CO2 Electroreduction to C2+ Products.

Developing electrocatalytic reactions with high-efficiency can make important contributions to carbon neutrality. However, poor long-term stability of catalysts is a bottleneck for its practical application. Herein, an "in situ periodic regeneration of catalyst (PR-C)" strategy is proposed to give long-term high efficiency of CO2 electroreduction to generate C2+ products over Cu catalyst by applying a positive potential pulse for a short time periodically in the halide-containing electrolyte. The high Faradaic efficiency (81.2 %) and current density (22.6 mA cm-2 ) could be maintained completely at least 36 h, while the activity and selectivity decreased continuously without using the PR-C method. Control experiments and operando characterization demonstrated that the surface structure and oxidation state of Cu could be recovered periodically by the PR-C method, which was beneficial for CO2 activation and C-C coupling.

CO2 electrolysis to multi-carbon products in strong acid at ampere-current levels on La-Cu spheres with channels.

Achieving satisfactory multi-carbon (C2+) products selectivity and current density under acidic condition is a key issue for practical application of electrochemical CO2 reduction reaction (CO2RR), but is challenging. Herein, we demonstrate that combining microenvironment modulation by porous channel structure and intrinsic catalytic activity enhancement via doping effect could promote efficient CO2RR toward C2+ products in acidic electrolyte (pH ≤ 1). The La-doped Cu hollow sphere with channels exhibits a C2+ products Faradaic efficiency (FE) of 86.2% with a partial current density of -775.8 mA cm-2. CO2 single-pass conversion efficiency for C2+ products can reach 52.8% at -900 mA cm-2. Moreover, the catalyst still maintains a high C2+ FE of 81.3% at -1 A cm-2. The channel structure plays a crucial role in accumulating K+ and OH- species near the catalyst surface and within the channels, which effectively suppresses the undesired hydrogen evolution and promotes C-C coupling. Additionally, the La doping enhances the generation of *CO intermediate, and also facilitates C2+ products formation.

Efficient C-N coupling for urea electrosynthesis on defective Co3O4 with dual-functional sites.

Urea electrosynthesis under ambient conditions is emerging as a promising alternative to conventional synthetic protocols. However, the weak binding of reactants/intermediates on the catalyst surface induces multiple competing pathways, hindering efficient urea production. Herein, we report the synthesis of defective Co3O4 catalysts that integrate dual-functional sites for urea production from CO2 and nitrite. Regulating the reactant adsorption capacity on defective Co3O4 catalysts can efficiently control the competing reaction pathways. The urea yield rate of 3361 mg h-1 gcat-1 was achieved with a corresponding faradaic efficiency (FE) of 26.3% and 100% carbon selectivity at a potential of -0.7 V vs. the reversible hydrogen electrode. Both experimental and theoretical investigations reveal that the introduction of oxygen vacancies efficiently triggers the formation of well-matched adsorption/activation sites, optimizing the adsorption of reactants/intermediates while decreasing the C-N coupling reaction energy. This work offers new insights into the development of dual-functional catalysts based on non-noble transition metal oxides with oxygen vacancies, enabling the efficient electrosynthesis of essential C-N fine chemicals.

Zn-induced electron-rich Sn catalysts enable highly efficient CO2 electroreduction to formate.

Renewable-energy-driven CO2 electroreduction provides a promising way to address the growing greenhouse effect issue and produce value-added chemicals. As one of the bulk chemicals, formic acid/formate has the highest revenue per mole of electrons among various products. However, the scaling up of CO2-to-formate for practical applications with high faradaic efficiency (FE) and current density is constrained by the difficulty of precisely reconciling the competing intermediates (*COOH and HCOO*). Herein, a Zn-induced electron-rich Sn electrocatalyst was reported for CO2-to-formate with high efficiency. The faradaic efficiency of formate (FEformate) could reach 96.6%, and FEformate > 90% was maintained at formate partial current density up to 625.4 mA cm-1. Detailed study indicated that catalyst reconstruction occurred during electrolysis. With appropriate electron accumulation, the electron-rich Sn catalyst could facilitate the adsorption and activation of CO2 molecules to form a intermediate and then promoted the carbon protonation of to yield a HCOO* intermediate. Afterwards, the HCOO* → HCOOH* proceeded via another proton-coupled electron transfer process, leading to high activity and selectivity for formate production.

Atomically Dispersed Ni-Cu Catalysts for pH-Universal CO2 Electroreduction.

CO2 electroreduction is of great significance to reduce CO2 emissions and complete the carbon cycle. However, the unavoidable carbonate formation and low CO2 utilization efficiency in neutral or alkaline electrolytes hinder its application at commercial scale. The development of CO2 reduction under acidic conditions provides a promising strategy, but the inhibition of the hydrogen evolution reaction is difficult. Herein, the first work to design a Ni-Cu dual atom catalyst supported on hollow nitrogen-doped carbon is reported for pH-universal CO2 electroreduction to CO. The catalyst shows a high CO Faradaic efficiency of ≈99% in acidic, neutral, and alkaline electrolytes, and the partial current densities of CO reach 190 ± 11, 225 ± 10, and 489 ± 14 mA cm-2 , respectively. In particular, the CO2 utilization efficiency under acidic conditions reaches 64.3%, which is twice as high as that of alkaline conditions. Detailed study indicates the existence of electronic interaction between Ni and Cu atoms. The Cu atoms push the Ni d-band center further toward the Fermi level, thereby accelerating the formation of *COOH. In addition, operando characterizations and density functional theory calculation are used to elucidate the possible reaction mechanism of CO2 to CO under acidic and alkaline electrolytes.

Lignin-derived carbon nanosheets boost electrochemical reductive amination of pyruvate to alanine.

Efficient and sustainable amino acid synthesis is essential for industrial applications. Electrocatalytic reductive amination has emerged as a promising method, but challenges such as undesired side reactions and low efficiency persist. Herein, we demonstrated a lignin-derived catalyst for alanine synthesis. Carbon nanosheets (CNSs) were synthesized from lignin via a template-assisted method and doped with nitrogen and sulfur to boost reductive amination and suppress side reactions. The resulting N,S-co-doped carbon nanosheets (NS-CNSs) exhibited outstanding electrochemical performance. It achieved a maximum alanine Faradaic efficiency of 79.5%, and a yield exceeding 1,199 µmol h-1 cm-2 on NS-CNS, with a selectivity above 99.9%. NS-CNS showed excellent durability during long-term electrolysis. Kinetic studies including control experiments and theoretical calculations provided further insights into the reaction pathway. Moreover, NS-CNS catalysts demonstrated potential in upgrading real-world polylactic acid plastic waste, yielding value-added alanine with a selectivity over 75%.

Integration of plasma and electrocatalysis to synthesize cyclohexanone oxime under ambient conditions using air as a nitrogen source.

Direct fixation of N2 to N-containing value-added chemicals is a promising pathway for sustainable chemical manufacturing. There is extensive demand for cyclohexanone oxime because it is the essential feedstock of Nylon 6. Currently, cyclohexanone oxime is synthesized under harsh conditions that consume a considerable amount of energy. Herein, we report a novel approach to synthesize cyclohexanone oxime by in situ NO3- generation from air under ambient conditions. This process was carried out through an integrated strategy including plasma-assisted air-to-NOx and co-electrolysis of NOx and cyclohexanone. A high rate of cyclohexanone oxime formation at 20.1 mg h-1 cm-2 and a corresponding faradaic efficiency (FE) of 51.4% was achieved over a Cu/TiO2 catalyst, and the selectivity of cyclohexanone oxime was >99.9% on the basis of cyclohexanone. The C-N bond formation mechanism was examined by in situ experiments and theoretical calculations, which showed that cyclohexanone oxime forms through the reaction between an NH2OH intermediate and cyclohexanone.