Rational Construction of Heterostructured Cu3 P@TiO2 Nanoarray for High-Efficiency Electrochemical Nitrite Reduction to Ammonia

Construction of dual sites on FeS2 surface for enhanced electrocatalytic reduction of nitrite to ammonia

Cost-effective iron sulfides (FeS2) hold great potential as high-performance catalysts for NO2- electroreduction to NH3 (NO2ER), which is hindered by the weak NO2 activation. Herein, the design of nonmetal-doped FeS2 electrocatalysts was initially conducted by density functional theory (DFT) computations. We found that doping with different nonmetal atoms effectively not only regulates the electronic structures of the d-electrons of Fe atoms but also creates the unique p-d hybridized dual active sites, thereby boosting the efficient NO2 activation. Owing to the optimal NO2 adsorption strength, N-doped FeS2 demonstrates a low limiting potential for the NO2--to-NH3 conversion, thus significantly improving NO2ER activity. Direct experimental evidence was provided afterward: an NH3 yield rate of 424.5 μmol/hcm-2 with a 92.4 % Faradaic efficiency was achieved. Our findings not only suggest a promising NO2ER catalyst through theoretical computations to guide experiments but also provide a comprehensive understanding of the structure-properties relationship.

Modulation of Charge Redistribution in Heterogeneous CoSe-Ni0.95Se Coupling with Ti3C2Tx MXene for Hydrazine-Assisted Water Splitting

Integrating abundant dual sites of hydrazine oxidation reaction (HzOR) and hydrogen evolution reaction (HER) into one catalyst is extremely urgent toward energy-saving H2 production. Herein, CoSe-Ni0.95Se heterostructure coupling with Ti3C2Tx MXene (CoSe-Ni0.95Se/MXene) is fabricated on nickel foam (NF) to enhance the catalytic performance. The heterogeneous CoSe-Ni0.95Se and MXene coupling effect can change the coordination of Ni and Co, resulting in adjusted interfacial electronic field and enhanced electron transfer from Ni0.95Se to CoSe especially near MXene surface. Also, the appearance of MXene can anchor more active sites, thereby abundant nucleophilic CoSe and electrophilic Ni0.95Se are formed induced by the charge redistribution, which can tailor d-band center, moderate *H adsorption free energy (∆GH *) and facilitate adsorption/desorption for hydrazine intermediates, contributing to much enhanced HER and HzOR performance. For example, the low potentials of -160.8 and 116.1 mV at 400 mA cm-2 are seen for HER and HzOR with long-term stability of 7 days. When assembled as overall hydrazine splitting (OHzS), a small cell voltage of 0.35 V to drive 100 mA cm-2 is obtained. Such concept of integrating abundant nucleophilic and electrophilic dual sites and regulating their d-band centers can offer in-depth understandings to design efficient bifunctional HER and HzOR electrocatalysts.

Recent progress on Ti-based catalysts in the electrochemical synthesis of ammonia

Electrochemical ammonia synthesis presents a sustainable alternative, offering the potential for enhanced energy efficiency and environmental benefits compared to the conventional Haber-Bosch process. In recent years, the electrocatalytic reduction of nitrate to ammonia (NO3-RR) has emerged as a crucial approach for achieving sustainable NH3 production. To enhance energy efficiency and successfully convert NO3- to NH3, it is essential to investigate cost-effective electrocatalysts that provide high Faraday efficiency and demonstrate adequate stability. Ti-based materials are considered ideal candidates as catalysts due to their environmental friendliness and robust stability. This review initially summarizes the nitrate reduction reaction pathway and concisely discusses the impact of the potential intermediates and reaction steps on the overall reaction efficiency and product selectivity. Subsequently, an overview of the fundamental characteristics of Ti and TiO2 is presented. Additionally, the research process on Ti-based electrocatalysts in the electrochemical reduction of nitrate for ammonia synthesis is summarized. Finally, the design strategies, such as heteroatom doping and the introduction of oxygen vacancies, to enhance catalytic efficiency and selectivity are presented. Through this comprehensive review, we endeavor to furnish researchers with the most recent insights into the application of titanium-based electrocatalysts in nitrate reduction reactions and to stimulate innovative thought processes on the electrocatalytic synthesis of ammonia.

Distinctive p-d Orbital Hybridization in CuSb Porous Nanonetworks for Enhanced Nitrite Electroreduction to Ammonia

Electrochemical nitrite reduction reaction (NO 2 - RR ${\mathrm{NO}}_{\mathrm{2}}^{\mathrm{ - }}{\mathrm{RR}}$ ), as a green and sustainable ammonia synthesis technology, has broad application prospects and environmental friendliness. Herein, an unconventional p-d orbital hybridization strategy is reported to realize the fabrication of defect-rich CuSb porous nanonetwork (CuSb PNs) electrocatalyst forNO 2 - RR ${\mathrm{NO}}_{\mathrm{2}}^ - {\mathrm{RR}}$ . The crystalline/amorphous heterophase structure is cleverly introduced into the porous nanonetworks, and this defect-rich structure exposes more atoms and activated boundaries. CuSb PNs exhibit a large NH3 yield (r N H 3 ${{r}_{{\mathrm{N}}{{{\mathrm{H}}}_{\mathrm{3}}}}}$ ) of 946.1 µg h-1m cat - 1 ${\mathrm{m}}_{{\mathrm{cat}}}^{ - {\mathrm{1}}}$ and a high faradaic efficiency (FE) of 90.7%. Experimental and theoretical studies indicate that the excellent performance of CuSb PNs results from the defect-rich porous nanonetworks structure and the p-d hybridization of Cu and Sb elements. This work describes a powerful pathway for the fabrication of p-d orbital hybrid defect-rich porous nanonetworks catalysts, and provides hope for solving the problem of nitrogen oxide pollution in the field of environment and energy.

Deciphering Indirect Nitrite Reduction to Ammonia in High-Entropy Electrocatalysts Using In Situ Raman and X-ray Absorption Spectroscopies

This research adopts a new method combining calcination and pulsed laser irradiation in liquids to induce a controlled phase transformation of Fe, Co, Ni, Cu, and Mn transition-metal-based high-entropy Prussian blue analogs into single-phase spinel high-entropy oxide and face-centered cubic high-entropy alloy (HEA). The synthesized HEA, characterized by its highly conductive nature and reactive surface, demonstrates exceptional performance in capturing low-level nitrite (NO2 -) in an electrolyte, which leads to its efficient conversion into ammonium (NH4 +) with a Faradaic efficiency of 79.77% and N selectivity of 61.49% at -0.8 V versus Ag/AgCl. In addition, the HEA exhibits remarkable durability in the continuous nitrite reduction reaction (NO2 -RR), converting 79.35% of the initial NO2 - into NH4 + with an impressive yield of 1101.48 µm h-1 cm-2. By employing advanced X-ray absorption and in situ electrochemical Raman techniques, this study provides insights into the indirect NO2 -RR, highlighting the versatility and efficacy of HEA in sustainable electrochemical applications.

P-Block Antimony-Copper Single-Atom Alloys for Selective Nitrite Electroreduction to Ammonia

Electrocatalytic reduction of NO2- to NH3 (NO2RR) offers an effective method for alleviating NO2- pollution and generating valuable NH3. Herein, a p-block single-atom alloy, namely, isolated Sb alloyed in a Cu substrate (Sb1Cu), is explored as a durable and high-current-density NO2RR catalyst. As revealed by the theoretical calculations and operando spectroscopic measurements, we demonstrate that Sb1 incorporation can not only hamper the competing hydrogen evolution reaction but also optimize the d-band center of Sb1Cu and intermediate adsorption energies to boost the protonation energetics of NO2--to-NH3 conversion. Consequently, Sb1Cu integrated in a flow cell achieves an outstanding NH3 yield rate of 2529.4 μmol h-1 cm-2 and FENH3 of 95.9% at a high current density of 424.2 mA cm-2, as well as a high durability for 100 h of electrolysis.

Electrocatalytic nitrite reduction to ammonia on an Rh single-atom catalyst

Electrocatalytic NO2- reduction to NH3 (NO2RR) holds great promise as a green method for high-efficiency NH3 production. Herein, an Rh single-atom catalyst where isolated Rh supported on defective BN nanosheets (Rh1/BN) is reported to exhibit the exceptional NO2RR activity and selectivity. Extensive experimental and theoretical studies unveil that the high NO2RR performance of Rh1/BN arises from the single-atom Rh sites, which not only promote the activation and hydrogenation of NO2--to-NH3 process, but also hamper the undesired hydrogen evolution. Consequently, Rh1/BN assembled in a flow cell exhibits the highest NH3 yield rate of 2165.4 μmol h-1 cm-2 and FENH3 of 97.83 % at a high current density of 355.7 mA cm-2, ranking it the most efficient catalysts for NO2--to-NH3 conversion.

Unveiling Cutting-Edge Developments in Electrocatalytic Nitrate-to-Ammonia Conversion

The excessive enrichment of nitrate in the environment can be converted into ammonia (NH3) through electrochemical processes, offering significant implications for modern agriculture and the potential to reduce the burden of the Haber-Bosch (HB) process while achieving environmentally friendly NH3 production. Emerging research on electrocatalytic nitrate reduction (eNitRR) to NH3 has gained considerable momentum in recent years for efficient NH3 synthesis. However, existing reviews on nitrate reduction have primarily focused on limited aspects, often lacking a comprehensive summary of catalysts, reaction systems, reaction mechanisms, and detection methods employed in nitrate reduction. This review aims to provide a timely and comprehensive analysis of the eNitRR field by integrating existing research progress and identifying current challenges. This review offers a comprehensive overview of the research progress achieved using various materials in electrochemical nitrate reduction, elucidates the underlying theoretical mechanism behind eNitRR, and discusses effective strategies based on numerous case studies to enhance the electrochemical reduction from NO3 - to NH3. Finally, this review discusses challenges and development prospects in the eNitRR field with an aim to guide design and development of large-scale sustainable nitrate reduction electrocatalysts.

RhNi Bimetallenes with Lattice-Compressed Rh Skin towards Ultrastable Acidic Nitrate Electroreduction

Harvesting recyclable ammonia (NH3 ) from acidic nitrate (NO3 - )-containing wastewater requires the utilization of corrosion-resistant electrocatalytic materials with high activity and selectivity towards acidic electrochemical nitrate reduction (NO3 ER). Herein, ultrathin RhNi bimetallenes with Rh-skin-type structure (RhNi@Rh BMLs) are fabricated towards acidic NO3 ER. The Rh-skin atoms on the surface of RhNi@Rh BMLs experience the lattice compression-induced strain effect, resulting in shortened Rh-Rh bond and downshifted d-band center. Experimental and theoretical calculation results corroborate that Rh-skin atoms can inhibit NO2 */NH2 * adsorption-induced Rh dissolution, contributing to the exceptional electrocatalytic durability of RhNi@Rh BMLs (over 400 h) towards acidic NO3 ER. RhNi@Rh BMLs also reveal an excellent catalytic performance, boasting a 98.4% NH3 Faradaic efficiency and a 13.4 mg h-1 mgcat -1 NH3 yield. Theoretical calculations reveal that compressive stress tunes the electronic structure of Rh skin atoms, which facilitates the reduction of NO* to NOH* in NO3 ER. The practicality of RhNi@Rh BMLs has also been confirmed in an alkaline-acidic hybrid zinc-nitrate battery with a 1.39 V open circuit voltage and a 10.5 mW cm-2 power density. This work offers valuable insights into the nature of electrocatalyst deactivation behavior and guides the development of high-efficiency corrosion-resistant electrocatalysts for applications in energy and environment.

Electrocatalytic reduction of nitrite to ammonia on undercoordinated Cu

Electrocatalytic NO2--to-NH3 reduction (NO2RR) has emerged as an intriguing route for simultaneous mitigation of harmful nitrites and production of valuable NH3. Herein, we design for the first time undercoordinated Cu nanowires (u-Cu) as an efficient and selective NO2RR electrocatalyst, delivering the maximum NO2--to-NH3 faradaic efficiency of 94.7% and an ammonia production rate of 494.5 μmol h-1 cm-2 at -0.7 V vs. RHE. Theoretical calculations reveal that the created undercoordinated Cu sites on u-Cu can enhance NO2- adsorption, boost NO2--to-NH3 energetics and restrict competitive hydrogen evolution, thereby enabling the active and selective NO2RR.

Electrochemical reduction of nitrite to ammonia on amorphous MoO3 nanosheets

Electrocatalytic NO2- reduction to NH3 (NO2RR) is an appealing approach for mitigating NO2- pollution and for the synthesis of valuable NH3, and so the exploration for high-performance NO2RR catalysts is pivotal yet remains challenging. Herein, amorphous MoO3 nanosheets (am-MoO3) were designed as a high-performance NO2RR electrocatalyst, delivering a maximum NO2--to-NH3 faradaic efficiency of 94.8% and NH3 yield rate of 480.4 μmol h-1 cm-2 at -0.6 V vs. RHE. Theoretical computations revealed that the largely enhanced NO2RR activity of am-MoO3 originated from the amorphization-induced O-vacancies, which could enhance the NO2--to-NH3 reaction energetics and hamper the competitive hydrogen evolution.

Promoting Nitrite-to-Ammonia Electroreduction over Amorphous CoS2 Nanorods

Electrocatalytic nitrite reduction to ammonia (NO2RR) emerges as a promising route to simultaneously attain harmful NO2- removal and green NH3 synthesis. In this study, amorphous CoS2 nanorods (a-CoS2) are first demonstrated as an effective NO2RR catalyst, which exhibits the maximum FENH3 of 88.7% and NH3 yield rate of 438.1 μmol h-1 cm-2 at -0.6 V vs RHE. Detailed experimental and computational investigations reveal that the high NO2RR performance of a-CoS2 originates from the amorphization-induced S vacancies to facilitate NO2- activation and hydrogenation, boost the electron transport kinetics, and inhibit the competitive hydrogen evolution.

Atomically dispersed Pd on defective BN nanosheets for nitrite electroreduction to ammonia

Electrocatalytic NO2- reduction to NH3 (NO2RR) offers a prospective strategy to concurrently achieve polluted NO2- removal and effective NH3 electrosynthesis. In this work, we report atomically dispersed Pd on defective BN nanosheets (Pd1/BN) as an efficient catalyst for the NO2RR, achieving the highest NH3-Faradaic efficiency of 91.7% with an NH3 yield rate of 347.1 μmol h-1 cm-2 at -0.6 V vs. RHE, superior to those of most previously reported electrocatalysts. Theoretical computations reveal the isolated Pd sites as catalytic centers to selectively adsorb NO2- and accelerate NO2--to-NH3 hydrogenation process with a minimized reaction barrier, eventually contributing to the considerably enhanced NO2RR selectivity and activity of Pd1/BN.

Electrocatalytic nitrite-to-ammonia reduction on isolated Cu sites

We report that isolated Cu atoms anchored on MnO2 nanowires (Cu1/MnO2) can be an effective catalyst towards the electrocatalytic NO2--to-NH3 reduction (NO2RR). A combination of experiments and theoretical calculations reveals that isolated Cu sites can effectively activate NO2-, lower the energy barrier of *NO→*NOH rate-determining step and suppress the competitive hydrogen evolution, thus facilitating both activity and selectivity towards the NO2RR. As a result, Cu1/MnO2 shows the maximum NH3-Faradaic efficiency of 93.3% with a corresponding NH3 yield rate of 439.8 μmol h-1 cm-2 at -0.7 V vs. RHE, together with an excellent electrocatalytic durability.

S-scheme Cu3P/TiO2 heterojunction for outstanding photocatalytic water splitting

TiO2 photocatalysts are of great interest in the fields of environmental purification, new energy and so on, because of their non-toxicity, high stability, high redox ability and low cost. However, the photogenerated carriers are severely recombined, which limits the application of TiO2 photocatalysts. Herein, S-scheme Cu3P/TiO2 heterojunction composites were successfully synthesized by a simple and efficient microwave hydrothermal method, and the results show that the hydrogen production rate of Cu3P/TiO2 is 5.83 mmol∙g-1∙h-1 under simulated sunlight irradiation, which is 7.3 and 83.3 times higher than that of pure TiO2 and Cu3P, respectively. This excellent performance is derived from the internal electric field (IEF) and energy band bending generated by the S-scheme heterojunction formed between Cu3P and TiO2. The density functional theory (DFT) calculation indicates that the Cu3P possess smaller work function and more negative conduction band (CB) position than that of TiO2, which is very conducive to greatly improve the H+ reduction ability and hydrogen production performance. This work provides a new idea for the reveal of electron transfer paths and active sites in S-scheme heterojunctions and deepens the mechanism understanding.

Single-atom Cu anchored on Mo2C boosts nitrite electroreduction to ammonia

We design single-atom Cu anchored on Mo2C (Cu1/Mo2C) as an effective electrocatalyst towards electrochemical nitrite reduction to ammonia (NO2RR), exhibiting an NH3-faradaic efficiency of 91.5% with a corresponding NH3 yield rate of 472.9 μmol h-1 cm-2 at -0.6 V vs. RHE. Theoretical computations unravel that single-atomic Cu couples with the surface Mo atom of Mo2C to enable the construction of Cu-Mo dual-active centers, which can synergistically activate NO2- and minimize the NO2--to-NH3 reaction energy barrier, whilst suppressing the competing hydrogen evolution reaction.

A Bi-Co Corridor Construction Effectively Improving the Selectivity of Electrocatalytic Nitrate Reduction toward Ammonia by Nearly 100

Improving the selective ammonia production capacity of electrocatalytic nitrate reduction reaction (NO3 RR) at ambient conditions is critical to the future development and industrial application of electrosynthesis of ammonia. However, the reaction involves multi-proton and electron transfer as well as the desorption and underutilization of intermediates, posing a challenge to the selectivity of NO3 RR. Here the electrodeposition site of Co is modulated by depositing Bi at the bottom of the catalyst, thus obtaining the Co+Bi@Cu NW catalyst with a Bi-Co corridor structure. In 50 mm NO3 - , Co+Bi@Cu NW exhibits a highest Faraday efficiency of ≈100% (99.51%), an ammonia yield rate of 1858.2 µg h-1  cm-2 and high repeatability at -0.6 V versus the reversible hydrogen electrode. Moreover, the change of NO2 - concentration on the catalyst surface observed by in situ reflection absorption imaging and the intermediates of the NO3 RR process detected by electrochemical in situ Raman spectroscopy together verify the NO2 - trapping effect of the Bi-Co corridor structure. It is believed that the measure of modulating the deposition site of Co by loading Bi element is an easy-to-implement general method for improving the selectivity of NH3 production as well as the corresponding scientific research and applications.

Nb-doped NiO nanoflowers for nitrite electroreduction to ammonia

Electrocatalytic reduction of nitrite to ammonia (NO2RR) is considered as an appealing route to simultaneously achieve sustainable ammonia production and abate hazardous nitrite pollution. Herein, atomically Nb-doped NiO nanoflowers are designed as a high-performance NO2RR catalyst, which exhibits the highest NH3-Faradaic efficiency of 92.4% with an NH3 yield rate of 200.5 μmol h-1 cm-2 at -0.6 V RHE. Theoretical calculations unravel that Nb dopants can act as Lewis acid sites to render effective NO2- activation, decreased protonation energy barriers, and restricted hydrogen evolution, ultimately leading to a high NO2RR selectivity and activity.