Electrocatalytic Reduction Research Articles

Rh, Co, and N-doped titanium mesh-based carbon nanosheet arrays for enhanced nitrite reduction reaction and ammonia generation

The electrocatalytic transformation of nitrite pollutants into valuable ammonia is crucial for the nitrogen cycle. However, the complex multi-reaction process necessitates the development of highly efficient and selective electrocatalysts. This study focuses on the creation of Rh-doped Co@NC anchored on a titanium mesh as an electrocatalyst to enhance the electrocatalytic nitrite reduction reaction (eNO2RR) for NH3 synthesis. By doping a trace amount of Rh within zeolitic imidazolate framework-67 nanosheets and subsequently pyrolyzing the material, uniformly distributed Rh and Co nanoparticles are anchored onto N-functionalized porous carbon nanosheet arrays. Consequently, the three-dimensional electrode enhances mass and electron transfer while providing abundant surface-exposed active sites for NH3 generation through eNO2RR. The Rh0.6 wt%–Co@NC/TM electrocatalyst, with a minimal Rh loading of 0.6 wt%, exhibits the highest Faradaic efficiency of 98.8 ± 0.7 % at −0.3 V, along with an NH3 yield of 1777.1 ± 7.0 μmol h−1 cm−2 at −0.7 V. Additionally, the electrocatalyst demonstrates exceptional durability over 20 consecutive cycles and remarkable environmental adaptability. Extensive experimental studies reveal that the superior performance of Rh0.6 wt%–Co@NC/TM arises from the synergistic catalysis between Co and Rh, which enhances NO2– adsorption and the production of active hydrogen for eNO2RR to NH3 synthesis. This research highlights that Rh incorporation facilitates the kinetics of eNO2RR and offers valuable insights for the development of efficient electrocatalysts towards NH3 synthesis.

Spin-mediated electrocatalytic nitrate reduction to ammonia on two-dimensional transition metal borides

Spin-mediated electrocatalytic nitrate reduction to ammonia on two-dimensional transition metal borides

Synergistic integration of copper and cobalt-MOF for high-efficiency electrocatalytic nitrate reduction to ammonia

Synergistic integration of copper and cobalt-MOF for high-efficiency electrocatalytic nitrate reduction to ammonia

Carbon dots-boosted active hydrogen for efficient electrocatalytic reduction of nitrate to ammonia

Carbon dots-boosted active hydrogen for efficient electrocatalytic reduction of nitrate to ammonia

Samarium as a Catalytic Electron-Transfer Mediator in Electrocatalytic Nitrogen Reduction to Ammonia.

Samarium diiodide (SmI2) exhibits high selectivity for N2R catalyzed by molybdenum complexes; however, it has so far been employed only as a stoichiometric reagent (0.3 equiv of NH3 per Sm) combined with coordinating proton sources (e.g., H2O, ROH). The latter inhibit catalytic turnover of SmIII owing to buildup of stable hydroxide/alkoxide sinks. Here, we report a tandem Sm/Mo-catalyzed eN2R system that achieves the lowest overpotential and highest Faradaic efficiency (82%) reported to date for nonaqueous eN2R at ambient pressure. Up to 8.4 equiv of NH3 is produced per Sm, representing a 25-fold increase over N2R with stoichiometric SmI2. A noncoordinating proton source enables electrochemical SmI3/SmI2 cycling at the applied potential of -1.45 V vs Fc+/0.

Ferromagnetic Fe-TiO2 spin catalysts for enhanced ammonia electrosynthesis

Magnetic field effects (MFE) of ferromagnetic spin electrocatalysts have attracted significant attention due to their potential to enhance catalytic activity under an external magnetic field. However, no ferromagnetic spin catalysts have demonstrated MFE in the electrocatalytic reduction of nitrate for ammonia (NO3RR), a pioneering approach towards NH3 production involving the conversion from diamagnetic NO3− to paramagnetic NO. Here, we report the ferromagnetic Fe-TiO2 to investigate MFE on NO3RR. Fe-TiO2 possesses a high density of atomically dispersed Fe sites and exhibits an intermediate-spin state, resulting in magnetic ordering through ferromagnetism. Assisted by a magnetic field, Fe-TiO2 achieves a Faradaic efficiency (FE) of up to 97% and an NH3 yield of 24.69 mg mgcat−1 at −0.5 V versus reversible hydrogen electrode. Compared to conditions without an external magnetic field, the FE and NH3 yield for Fe-TiO2 under an external magnetic field is increased by ~21.8% and ~ 3.1 times, respectively. In-situ characterization and theoretical calculations show that spin polarization enhances the critical step of NO hydrogenation to NOH by optimizing electron transfer pathways between Fe and NO, significantly boosting NO3RR activity.

Co-Doped CuO Nanoarrays for Enhanced Electrocatalytic Nitrate Reduction to Ammonia via Active Hydrogen Regulation

Co-Doped CuO Nanoarrays for Enhanced Electrocatalytic Nitrate Reduction to Ammonia via Active Hydrogen Regulation

Computational Modeling of Electrocatalysts for CO2 Reduction: Probing the Role of Primary, Secondary, and Outer Coordination Spheres.

ConspectusIn the search for efficient and selective electrocatalysts capable of converting greenhouse gases to value-added products, enzymes found in naturally existing bacteria provide the basis for most approaches toward electrocatalyst design. Ni,Fe-carbon monoxide dehydrogenase (Ni,Fe-CODH) is one such enzyme, with a nickel-iron-sulfur cluster named the C-cluster, where CO2 binds and is converted to CO at high rates near the thermodynamic potential. In this Account, we divide the enzyme's catalytic contributions into three categories based on location and function. We also discuss how computational techniques provide crucial insight into implementing these findings in homogeneous CO2 reduction electrocatalysis design principles. The CO2 binding sites (e.g., Ni and "unique" Fe ion) along with the ligands that support it (e.g., iron-sulfur cluster) form the primary coordination sphere. This is replicated in molecular electrocatalysts via the metal center and ligand framework where the substrate binds. This coordination sphere has a direct impact on the electronic configuration of the catalyst. By computationally modeling a series of Ni and Co complexes with bipyridyl-N-heterocyclic carbene ligand frameworks of varying degrees of planarity, we were able to closely examine how the primary coordination sphere controls the product distribution between CO and H2 for these catalysts. The secondary coordination sphere (SCS) of Ni,Fe-CODH contains residues proximal to the active site pocket that provide hydrogen-bonding stabilizations necessary for the reaction to proceed. Enhancing the SCS when synthesizing new catalysts involves substituting functional groups onto the ligand for direct interaction with the substrate. To analyze the endless possible substitutions, computational techniques are ideal for deciphering the intricacies of substituent effects, as we demonstrated with an array of imidazolium-functionalized Mn and Re bipyridyl tricarbonyl complexes. By examining how the electrostatic interactions between the ligand, substrate, and proton source lowered activation energy barriers, we determined how best to pinpoint the SCS additions. The outer coordination sphere comprises the remaining parts of Ni,Fe-CODH, such as the elaborate protein matrix, solvent interactions, and remote metalloclusters. The challenge in elucidating and replicating the role of the vast protein matrix has understandably led to a localized focus on the primary and secondary coordination spheres. However, certain portions of Ni,Fe-CODH's expansive protein scaffold are suggested to be catalytically relevant despite considerable distance from the active site. Closer studies of these relatively overlooked areas of nature's exceptionally proficient catalysts may be crucial to continually improve upon electrocatalysis protocols. Mechanistic analysis of cobalt phthalocyanines (CoPc) immobilized onto carbon nanotubes (CoPc/CNT) reveals how the active site microenvironment and outer coordination sphere effects unlock the CoPc molecule's previously inaccessible intrinsic catalytic ability to convert CO2 to MeOH. Our research suggests that incorporating the three coordination spheres in a holistic approach may be vital for advancing electrocatalysis toward viability in mitigating climate disruption. Computational methods allow us to closely examine transition states and determine how to minimize key activation energy barriers.

Microenvironment engineering by targeted delivery of Ag nanoparticles for boosting electrocatalytic CO2 reduction reaction

Creating and maintaining a favorable microenvironment for electrocatalytic CO2 reduction reaction (eCO2RR) is challenging due to the vigorous interactions with both gas and electrolyte solution during the electrocatalysis. Herein, to boost the performance of eCO2RR, a unique synthetic method that deploys the in situ reduction of precoated precursors is developed to produce activated Ag nanoparticles (NPs) within the gas diffusion layer (GDL), where the thus-obtained Ag NPs-Skeleton can block direct contact between the active Ag sites and electrolyte. Specifically, compared to the conventional surface loading mode in the acidic media, our freestanding and binder free electrode can achieve obvious higher CO selectivity of 94%, CO production rate of 23.3 mol g−1 h−1, single-pass CO2 conversion of 58.6%, and enhanced long-term stability of 8 hours. Our study shows that delivering catalysts within the GDL does not only gain the desired physical protection from GDL skeleton to achieve a superior local microenvironment for more efficient pH-universal eCO2RR, but also manifests the pore structures to effectively address gas accumulation and flood issues.

Gold Single Atom Doped Defective Nanoporous Copper Octahedrons for Electrocatalytic Reduction of Carbon Dioxide to Ethylene.

Electrocatalytic CO2 reduction into high-value multicarbon products offers a sustainable approach to closing the anthropogenic carbon cycle and contributing to carbon neutrality, particularly when renewable electricity is used to power the reaction. However, the lack of efficient and durable electrocatalysts with high selectivity for multicarbons severely hinders the practical application of this promising technology. Herein, a nanoporous defective Au1Cu single-atom alloy (De-Au1Cu SAA) catalyst is developed through facile low-temperature thermal reduction in hydrogen and a subsequent dealloying process, which shows high selectivity toward ethylene (C2H4), with a Faradaic efficiency of 52% at the current density of 252 mA cm-2 under a potential of -1.1 V versus reversible hydrogen electrode (RHE). In situ spectroscopy measurements and density functional theory (DFT) calculations reveal that the high C2H4 product selectivity results from the synergistic effect between Au single atoms and defective Cu sites on the surface of catalysts, where Au single atoms promote *CO generation and Cu defects stabilize the key intermediate *OCCO, which altogether enhances C-C coupling kinetics. This work provides important insights into the catalyst design for electrochemical CO2 reduction to multicarbon products.

The Graphene Oxide/Gold Nanoparticles Hybrid Layers for Hydrogen Peroxide Sensing—Effect of the Nanoparticles Shape and Importance of the Graphene Oxide Defects for the Sensitivity

Graphene oxide (GO) and reduced graphene oxides (RGOs) show intrinsic electrocatalytic activity towards the electrocatalytic reduction of H2O2. Combining these materials with gold nanoparticles results in highly sensitive electrodes, with sensitivity in the nanomolar range because the electrocatalytic properties of GO and nanoparticles are synergistically enhanced. Understanding the factors influencing such synergy is crucial to designing novel catalytically active materials. In this contribution, we study gold nanostructures having shapes of nanospheres (AuNSs), nanourchins (AuNUs), and nanobowls (AuNBs) combined with GO or electrochemically reduced graphene oxide (ERGO). We investigate the amperometric responses of the hybrid layers to H2O2. The AuNUs show the highest sensitivity compared to AuNBs and AuNSs. All materials are characterized by electron microscopy and Raman spectroscopy. Raman spectra are deconvoluted by fitting them with five components in th e1000–1800 cm−1 range (D*, D, D”, G, and D′). The interaction between nanoparticles and GO is visualized by the relative intensities of Raman bands (ID/IG) and other parameters in the Raman spectra, like various D”, D* band positions and intensities. The ID/IG parameter is linearly correlated with the sensitivity (R2 = 0.97), suggesting that defects in the graphene structure are significant factors influencing the electrocatalytic H2O2 reduction.

Tuning the Acid Hardness Nature of Cu Catalyst for Selective Nitrate‐to‐Ammonia Electroreduction

Electrocatalytic nitrate reduction reaction (NO3RR) in alkaline electrolyte presents a sustainable pathway for energy storage and green ammonia (NH3) synthesis. However, it remains challenging to obtain high activity and selectivity due to the limited protonation and/or desorption processes of key intermediates. Herein, we propose a strategy to regulate the acid hardness nature of Cu catalyst by introducing appropriate modifier. Using density functional theory calculations, we firstly identified that the BaO‐modified Cu showed optimal Gibbs free energies for key NO3RR steps, including the protonation of *NO and the desorption of *NH3. Experimentally, the BaO‐modified Cu catalyst exhibited 97.3% Faradaic efficiency (FE) for NH3 with a yield rate of 356.9 mmol h‐1 gcat‐1. It could also maintain high activity across a wide range of applied potentials and nitrate substrate concentrations. Detailed experimental and theoretical studies revealed that the Ba species could modulate the local electronic states of Cu, enhance the electron transfer rate, and optimize the adsorption/protonation/desorption processes of the N‐containing intermediates, leading to the excellent catalytic performance for NO3‐‐to‐NH3.

Tuning the Acid Hardness Nature of Cu Catalyst for Selective Nitrate-to-Ammonia Electroreduction.

Electrocatalytic nitrate reduction reaction (NO3RR) in alkaline electrolyte presents a sustainable pathway for energy storage and green ammonia (NH3) synthesis. However, it remains challenging to obtain high activity and selectivity due to the limited protonation and/or desorption processes of key intermediates. Herein, we propose a strategy to regulate the acid hardness nature of Cu catalyst by introducing appropriate modifier. Using density functional theory calculations, we firstly identified that the BaO-modified Cu showed optimal Gibbs free energies for key NO3RR steps, including the protonation of *NO and the desorption of *NH3. Experimentally, the BaO-modified Cu catalyst exhibited 97.3% Faradaic efficiency (FE) for NH3 with a yield rate of 356.9 mmol h-1 gcat-1. It could also maintain high activity across a wide range of applied potentials and nitrate substrate concentrations. Detailed experimental and theoretical studies revealed that the Ba species could modulate the local electronic states of Cu, enhance the electron transfer rate, and optimize the adsorption/protonation/desorption processes of the N-containing intermediates, leading to the excellent catalytic performance for NO3--to-NH3.

Modulating the Coordination Environment of Atomically Dispersed Nickel for Efficient Electrocatalytic CO2 Reduction at Low Overpotentials and Industrial Current Densities.

Electrocatalytic CO2-to-CO conversion with a high CO Faradaic efficiency (FECO) at low overpotentials and industrial-level current densities is highly desirable but a huge challenge over non-noble metal catalysts. Herein, graphitic N-rich porous carbons supporting atomically dispersed nickel (NiN4-O sites with an axial oxygen) were synthesized (denoted as O-Ni-Nx-GC) and applied as the cathode catalyst in a CO2RR flow cell. O-Ni-Nx-GC showed excellent selectivity with a FECO over 92% at low overpotentials ranging from 17 to 60 mV, and over 99% at 80 mV. The FECO was ∼100% at industrial-level current densities from 200 to 900 mA·cm-2. Impressively, O-Ni-Nx-GC delivered a state-of-the-art FECO of >96% at 1 A·cm-2 with a turnover frequency of 81.5 s-1 in a 1 M KOH electrolyte. O-Ni-Nx-GC offered excellent stability during long-term operation for 140 h at 100 mA·cm-2, maintaining a FECO > 99%. Mechanism studies revealed that the axial oxygen at the atomically dispersed nickel sites enhanced electron delocalization, with the graphitic N-rich porous carbon support lowering the CO2-to-CO energy barrier and inducing a negative shift in the Ni-3d d-band center, effectively promoting the formation of the *COOH intermediate while weakening the adsorption of the *CO intermediate, thus optimizing the catalytic activity/selectivity to CO under practical conditions.

Ni Single Atoms/Fe3N Nanoparticles Supported by N-Doped Carbon Hollow Nanododecahedras with Nanotubes on the Surface for Efficient Electro-Reduction of CO2 to CO.

The transition metal single atoms (SAs)-based catalysts with M-NX coordination environment have shown excellent performance in electrocatalytic reduction of CO2, and they have received extensive attention in recent years. However, the presence of SAs makes it very difficult to efficiently improve the coordination environment. In this paper, a method of direct high-temperature pyrolysis carbonization of ZIF-8 adsorbed with Ni2+ and Fe2+ ions is reported for the synthesis of Ni SAs and Fe3N nanoparticles (NPs) supported by the N-doped carbon (NC) hollow nanododecahedras (HNDs) with nanotubes (NTs) on the surface (Ni SAs/Fe3N NPs@NC-HNDs-NTs). The synergistic effect between Ni SAs and Fe3N NPs can obviously improve the proton-coupled electron transfer step of CO2 reduction reaction and promotes the process of electrocatalytic reduction of CO2 to CO. The fabricated Ni SAs/Fe3N NPs@NC-HNDs-NTs exhibits a high CO selectivity of up to 94% in the potential range of -0.41--0.81 V versus Reversible Hydrogen Electrode (vs RHE), and an optimal CO Faraday efficiency (FECO) of ≈97.31% at -0.68 V (vs RHE) in the reduction reaction CO2 to CO. In the theoretical calculation results, due to the non-bonding synergy effect between Ni SAs and Fe3N NPs, the free energy of *COOH formation is greatly reduced and the adsorption of *CO is obviously improved, which will efficiently promote the conversion between the intermediates in the reaction step and accelerate electro-reduction process of CO2. This work will provide a new method for constructing a mutually optimized coordination environment between Ni SAs and Fe3N NPs to improve the catalytic performance of CO2RR by synergistic complementarity between the dual active sites.

Hinged Carboxylate in the Artificial Distal Pocket of an Iron Porphyrin Enhances CO2 Electroreduction at Low Overpotential.

To efficiently capture, activate, and transform small molecules, metalloenzymes have evolved to integrate a well-organized pocket around the active metal center. Within this cavity, second coordination sphere functionalities are precisely positioned to optimize the rate, selectivity, and energy cost of catalytic reactions. Inspired by this strategy, an artificial distal pocket defined by a preorganized 3D strap is introduced on an iron-porphyrin catalyst (sc-Fe) for the CO2-to-CO electrocatalytic reduction. Combined electrochemical, kinetic, and computational studies demonstrate that the adequate positioning of a carboxylate/carboxylic group acting in synergy with a trapped water molecule within this distal pocket remarkably enhances the reaction turnover frequency (TOF) by four orders of magnitude compared to the perfluorinated iron-tetraphenylporphyrin catalyst (F20Fe) operating at a similar low overpotential. A proton-coupled electron transfer (PCET) is found to be the key process responsible for the unexpected protonation of the coordinating carboxylate, which, upon CO2 insertion, shifts from the first to the second coordination sphere to play a possible secondary role as a proton relay.

Microstructure Optimization of Nickel–Nitrogen‐Doped Porous Nanofibers for Enhanced Electrochemical CO2 Reduction

AbstractThe utilization of renewable energy for electrocatalytic CO2 reduction (CO2RR) represents a significant advancement in green carbon conversion technologies. Single atom catalysts (SACs) featuring a transition metal‐nitride‐carbon (M‐Nx‐C) architecture exhibit catalytic activity for the reduction of CO2 to CO. However, the impact of the morphology of carbon supports, particularly their pore structure, on the electrocatalytic performance of CO2RR warrants further investigation. In this study, we fabricated a series of Ni‐based SACs supported by porous carbon nanofibers through electrospinning and sacrificial template method. We examined variations in microstructure of these porous carbon nanofiber carriers at different pyrolysis temperatures and elucidated their effects on CO2RR catalytic performance. The catalyst obtained at 1000 °C demonstrated efficient electrocatalysis for converting CO2 to CO due to its large specific surface area, abundant hierarchical pore structure, and high content of Ni‐Nx species resulting from both the sacrificial template method and high‐temperature pyrolysis. A Faradaic efficiency exceeding 90% was sustained across potentials ranging from −0.7 V to −1.3 V (versus RHE), with a peak efficiency reaching 96.1% at −1.0 V (versus RHE). Kinetic analysis indicated that this sample exhibited the highest reaction kinetics alongside minimal charge transfer resistance.

Ammonia electrosynthesis from nitrate using a stable amorphous/crystalline dual-phase Cu catalyst

Renewable energy-driven electrocatalytic nitrate reduction reaction presents a low-carbon and sustainable route for ammonia synthesis under mild conditions. Yet, the practical application of this process is currently hindered by unsatisfactory electrocatalytic activity and long-term stability. Herein we achieve high-rate ammonia electrosynthesis using a stable amorphous/crystalline dual-phase Cu catalyst. The ammonia partial current density and formation rate reach 3.33 ± 0.005 A cm−2 and 15.5 ± 0.02 mmol h−1 cm−2 at a low cell voltage of 2.6 ± 0.01 V, respectively. Remarkably, the dual-phase Cu catalyst can maintain stable ammonia production with a Faradaic efficiency of around 90% at a high current density of 1.5 A cm−2 for up to 300 h. A scale-up demonstration with an electrode size of 100 cm2 achieves an ammonia formation rate as high as 11.9 ± 0.5 g h−1 at a total current of 160 A. The impressive electrocatalytic performance is ascribed to the presence of stable amorphous Cu domains which promote the adsorption and hydrogenation of nitrogen-containing intermediates, thus improving reaction kinetics for ammonia formation. This work underscores the importance of stabilizing metastable amorphous structures for improving electrocatalytic reactivity and long-term stability.

Built-in electric field in the Mn/C60 heterojunction promotes electrocatalytic nitrogen reduction to ammonia.

The electrochemical nitrogen reduction reaction (NRR) has been regarded as a green and promising alternative to the traditional Haber-Bosch process. However, the high bond energy (940.95 kJ mol-1) of the NN triple bond hinders the adsorption and activation of N2 molecules, which is a critical factor restricting the catalytic performance of catalysts and their large-scale applications. Herein, an Mn/C60 heterostructure is constructed via a simple grinding and calcination process and achieves an extraordinary faradaic efficiency of 42.18% and an NH3 yield rate of 14.52 μg h-1 mgcat-1 at -0.4 V vs. RHE in 0.08 M Na2HPO4. Our experimental and theoretical results solidly confirm that the spontaneous charge transfer at the Mn/C60 heterointerface promotes the formation of a built-in electric field, which facilitates the electron transfer from Mn towards C60 and creates localized electrophilic and nucleophilic regions. The formation of the space-charge region effectively optimized the adsorption energy of the key intermediate *NH-*NH2 and also reduced the free energy barrier for the hydrogenation step of *NH-*NH to *NH-*NH2. Furthermore, the calculated lower limiting potential (UL(NRR)) in Mn/C60 relative to the HER (UL(HER)) demonstrates its enhanced selectivity toward the NRR. This work provided new insights into enhancing the activity and performance of electrocatalysts for the NRR by constructing heterojunctions to improve nitrogen adsorption.

Advances in Electrocatalytic Nitrate Reduction: Insights into Mechanisms and Reaction Optimization

AbstractElectrocatalytic nitrate reduction (NO3RR) offers a promising approach to address nitrate pollution by converting harmful nitrates into environment‐benign or valuable products like nitrogen gas (N2) or ammonia (NH3). This review explores the mechanisms, challenges, and catalysts involved in NO3RR, highlighting the role of catalyst selectivity, stability, and external reaction conditions. The discussion also covers the environmental and economic benefits of NO3RR for water treatment, alongside potential future directions in scaling‐up, system integration, and expanding research into tackling related nitrogen‐based pollutants as well as real world applications.