Crystal‐Phase‐Engineered PdCu Electrocatalyst for Enhanced Ammonia Synthesis

Crystal phase engineering is a powerful strategy for regulating the performance of electrocatalysts towards many electrocatalytic reactions, while its impact on the nitrogen electroreduction has been largely unexplored. Herein, we demonstrate that structurally ordered body‐centered cubic (BCC) PdCu nanoparticles can be adopted as active, selective, and stable electrocatalysts for ammonia synthesis. Specifically, the BCC PdCu exhibits excellent activity with a high NH₃ yield of 35.7 μg h^?1 mg^?1_cat, Faradaic efficiency of 11.5 %, and high selectivity (no N₂H₄ is detected) at ?0.1 V versus reversible hydrogen electrode, outperforming its counterpart, face‐centered cubic (FCC) PdCu, and most reported nitrogen reduction reaction (NRR) electrocatalysts. It also exhibits durable stability for consecutive electrolysis for five cycles. Density functional theory calculation reveals that strong orbital interactions between Pd and neighboring Cu sites in BCC PdCu obtained by structure engineering induces an evident correlation effect for boosting up the Pd 4d electronic activities for efficient NRR catalysis. Our findings open up a new avenue for designing active and stable electrocatalysts towards NRR.     

Methane activation at low temperature in an acidic electrolyte using PdAu/C,PdCu/C,and PdTiO2/C electrocatalysts for PEMFC

Pd/C, PdAu/C, PdCu/C, and PdTiO₂/C electrocatalysts were prepared by a sodium borohydride reduction process for methane activation at low temperatures in a PEMFC reactor. These electrocatalysts were characterized by XRD, TEM, XPS, ICP-MS, ATR-FTIR, and cyclic voltammetry. The diffractograms of Pd/C, PdAu(50:50)/C, PdCu(50:50)/C, and PdTiO₂(50:50)/C electrocatalysts showed peaks associated with Pd face-centered cubic structure. PdAu(50:50)/C showed a small shift in the peak center when it was compared to Pd/C, while PdCu(50:50)/C showed a shift to higher angles when it was also compared to Pd/C. This effect can be due to the formation of an alloy between Pd and Au, and Pd and Cu. By TEM experiments, a mean nanoparticle size was observed between 6.9 and 8.9 nm for all electrocatalysts. Cyclic voltammograms of Pd/C, PdAu/C, PdCu/C and PdTiO₂/C electrocatalysts showed an increase in current density values after the adsorption of methane The ATR-FTIR experiments showed for all electrocatalysts the formation of methanol and formic acidic. Polarization curves at 80 °C acquired in a PEMFC reactor showed that PdAu(50:50)/C and PdTiO₂(50:50)/C had superior performance when compared to Pd/C, indicating the beneficial effect of adding the co-catalyst; this behavior has been attributed to the bifunctional mechanism or electronic effect.

     

A Facile Strategy to PdCu Bimetallic Alloy Nanosponges with Highly Porous Features as a High‐Performance Electrocatalytic Activity for Ethanol Electrooxidation in an Alkaline Medium

Well‐defined three‐dimensional (3D) PdCu bimetallic alloy nanosponges (BANs) with highly porous structure was reported through a rapid and general strategy. Significantly, the as‐prepared PdCu BANs exhibited greatly enhanced activity and stability than commercial Pd/C catalyst towards ethanol electrooxidation in an alkaline medium. Pd₁Cu₁ shows higher active area and better electrocatalytic activity than Pd₁Cu₂ and Pd₂Cu₁. This result demonstrates the potential of applying these PdCu BANs as effective electrocatalysts for direct alcohol fuel cells (DAFCs).     

Facile Synthesis of PdCu Echinus‐Like Nanocrystals as Robust Electrocatalysts for Methanol Oxidation Reaction

Exploiting high‐performance and inexpensive electrocatalysts for methanol electro‐oxidation is conductive to promoting the commercial application of direct methanol fuel cells. Here, we present a facile synthesis of echinus‐like PdCu nanocrystals (NCs) via a one‐step and template‐free method. The echinus‐like PdCu NCs possess numerous straight and long branches which can provide abundant catalytic active sites. Owing to the novel nanoarchitecture and electronic effect of the PdCu alloy, the echinus‐like PdCu NCs display high electrocatalytic performance toward methanol oxidation reaction in an alkaline medium. The mass activity of echinus‐like PdCu NCs is 1202.1 mA mg_Pd^?1, which is 3.7 times that of Pd/C catalysts. In addition, the echinus‐like structure, as a kind of three‐dimensional self‐supported nanoarchitecture, endows PdCu NCs with significantly enhanced stability and durability. Hence, the echinus‐like PdCu NCs hold prospect of being employed as electrocatalysts for direct alcohol fuel cells.     

Amorphous core/shell Ti-doped SnO2 with synergistically improved N2 adsorption/activation and electrical conductivity for electrochemical N2 reduction

Electrochemical nitrogen reduction reaction (NRR) has been considered as an appealing and sustainable method to produce ammonia from N₂ under ambient conditions, attracting increasing interest. Limited by low solubility of N₂ in water and high stability of NN triple bond, developing NRR electrocatalysts with both strong N₂ adsorption/activation and high electrical conductivity remain challenging. Here, we demonstrate an efficient strategy to develop NRR electrocatalyst with synergistically enhanced N₂ adsorption/activation and electrical conductivity by heteroatom doping. Combining computational and experimental study, the DFT-designed Ti-doped SnO₂ exhibits significantly enhanced NRR performance with ammonia yield rate of 13.09 µg h^?1 mg^?1 at ?0.2 V vs. RHE. Particularly, the Faradaic efficiency reaches up to 42.6%, outperforming most of Sn-based electrocatalysts. The fundamental mechanism for improving NRR performance of SnO₂ by Ti doping is also revealed. Our work highlights a powerful strategy for developing high-activity electrocatalysts for NRR and beyond.     

ZnO Quantum Dots Coupled with Graphene toward Electrocatalytic N2 Reduction: Experimental and DFT Investigations

Electrochemical reduction of N₂ to NH₃ is a promising method for artificial N₂ fixation, but it requires efficient and robust electrocatalysts to boost the N₂ reduction reaction (NRR). Herein, a combination of experimental measurements and theoretical calculations revealed that a hybrid material in which ZnO quantum dots (QDs) are supported on reduced graphene oxide (ZnO/RGO) is a highly active and stable catalyst for NRR under ambient conditions. Experimentally, ZnO/RGO was confirmed to favor N₂ adsorption due to the largely exposed active sites of ultrafine ZnO QDs. DFT calculations disclosed that the electronic coupling of ZnO with RGO resulted in a considerably reduced activation-energy barrier for stabilization of *N₂H, which is the rate-limiting step of the NRR. Consequently, ZnO/RGO delivered an NH₃ yield of 17.7 μg h⁻¹ mg⁻¹ and a Faradaic efficiency of 6.4 % in 0.1 m Na₂SO₄ at −0.65 V (vs. RHE), which compare favorably to those of most of the reported NRR catalysts and thus demonstrate the feasibility of ZnO/RGO for electrocatalytic N₂ fixation.     

Surface-Regulated Rhodium–Antimony Nanorods for Nitrogen Fixation

Surface regulation is an effective strategy to improve the performance of catalysts, but it has been rarely demonstrated for nitrogen reduction reaction (NRR) to date. Now, surface-rough Rh₂Sb nanorod (RNR) and surface-smooth Rh₂Sb NR (SNR) were selectively created, and their performance for NRR was investigated. The high-index-facet bounded Rh₂Sb RNRs/C exhibit a high NH₃ yield rate of 228.85±12.96 μg h⁻¹ mg⁻¹_Rh at −0.45 V versus reversible hydrogen electrode (RHE), outperforming the Rh₂Sb SNRs/C (63.07±4.45 μg h⁻¹ mg⁻¹_Rh) and Rh nanoparticles/C (22.82±1.49 μg h⁻¹ mg⁻¹_Rh), owing to the enhanced adsorption and activation of N₂ on high-index facets. Rh₂Sb RNRs/C also show durable stability with negligible activity decay after 10 h of successive electrolysis. The present work demonstrates that surface regulation plays an important role in promoting NRR activity and provides a new strategy for creating efficient NRR electrocatalysts.     

A Janus Fe-SnO2 Catalyst that Enables Bifunctional Electrochemical Nitrogen Fixation

Electrochemical N₂ reduction reactions (NRR) and the N₂ oxidation reaction (NOR), using H₂O and N₂, are a sustainable approach to N₂ fixation. To date, owing to the chemical inertness of nitrogen, emerging electrocatalysts for the electrochemical NRR and NOR at room temperature and atmospheric pressure remain largely underexplored. Herein, a new-type Fe-SnO₂ was designed as a Janus electrocatalyst for achieving highly efficient NRR and NOR catalysis. A high NH₃ yield of 82.7 μg h⁻¹ mg_cat.⁻¹ and a Faraday efficiency (FE) of 20.4 % were obtained for NRR. This catalyst can also serve as an excellent NOR electrocatalyst with a NO₃⁻ yields of 42.9 μg h⁻¹ mg_cat.⁻¹ and a FE of 0.84 %. By means of experiments and DFT calculations, it is revealed that the oxygen vacancy-anchored single-atom Fe can effectively adsorb and activate chemical inert N₂ molecules, lowering the energy barrier for the vital breakage of N≡N and resulting in the enhanced N₂ fixation performance.     

Highly Efficient Electrochemical Nitrate and Nitrogen Reduction to Ammonia under Ambient Conditions on Electrodeposited Cu-Nanosphere Electrode

The electrochemical reduction reaction of nitrogenous species such as NO₃⁻ (NO₃RR) and N₂ (NRR) is a promising strategy for producing ammonia under ambient conditions. However, low activity and poor selectivity of both NO₃RR and NRR remain the biggest problem of all current electrocatalysts. In this work, we fabricated Cu-nanosphere film with a high surface area and dominant with a Cu(200) facet by simple electrodeposition method. The Cu-nanosphere film exhibits high electrocatalytic activity for NO₃RR and NRR to ammonia under ambient conditions. In the nitrate environment, the Cu-nanosphere electrode reduced NO₃⁻ to yield NH₃ at a rate of 5.2 mg/h cm², with a Faradaic efficiency of 85 % at −1.3 V. In the N₂-saturated environment, the Cu-nanosphere electrode reduced N₂ to yield NH₃ with the highest yield rate of 16.2 μg/h cm² at −0.5 V, and the highest NH₃ Faradaic efficiency of 41.6 % at −0.4 V. Furthermore, the Cu-nanosphere exhibits excellent stability with the NH₃ yield rate, and the Faradaic efficiency remains stable after 10 consecutive cycles. Such high levels of NH₃ yield, selectivity, and stability at low applied potential are among the best values currently reported in the literature.     

Clean Synthesis of an Economical 3D Nanochain Network of PdCu Alloy with Enhanced Electrocatalytic Performance towards Ethanol Oxidation

A one‐pot method for the fast synthesis of a 3D nanochain network (NNC) of PdCu alloy without any surfactants is described. The composition of the as‐prepared PdCu alloy catalysts can be precisely controlled by changing the precursor ratio of Pd to Cu. First, the Cu content changes the electronic structure of Pd in the 3D NNC of PdCu alloy. Second, the 3D network structure offers large open pores, high surface areas, and self‐supported properties. Third, the surfactant‐free strategy results in a relatively clean surface. These factors all contribute to better electrocatalytic activity and durability towards ethanol oxidation. Moreover, the use of copper in the alloy lowers the price of the catalyst by replacing the noble metal palladium with non‐noble metal copper. The composition‐optimized Pd₈₀Cu₂₀ alloy in the 3D NNC catalyst shows an increased electrochemically active surface area (80.95 m² g^?1) and a 3.62‐fold enhancement of mass activity (6.16 A mg^?1) over a commercial Pd/C catalyst.     

Defect Engineering Metal‐Free Polymeric Carbon Nitride Electrocatalyst for Effective Nitrogen Fixation under Ambient Conditions

Electrocatalytic nitrogen reduction reaction (NRR) under ambient conditions provides an intriguing picture for the conversion of N₂ into NH₃. However, electrocatalytic NRR mainly relies on metal‐based catalysts, and it remains a grand challenge in enabling effective N₂ activation on metal‐free catalysts. Here we report a defect engineering strategy to realize effective NRR performance (NH₃ yield: 8.09 μg h^?1 mg^?1_cat., Faradaic efficiency: 11.59 %) on metal‐free polymeric carbon nitride (PCN) catalyst. Illustrated by density functional theory calculations, dinitrogen molecule can be chemisorbed on as‐engineered nitrogen vacancies of PCN through constructing a dinuclear end‐on bound structure for spatial electron transfer. Furthermore, the N?N bond length of adsorbed N₂ increases dramatically, which corresponds to “strong activation” system to reduce N₂ into NH₃. This work also highlights the significance of defect engineering for improving electrocatalysts with weak N₂ adsorption and activation ability.     

Vacancy Engineering of Iron-Doped W18O49 Nanoreactors for Low-Barrier Electrochemical Nitrogen Reduction

The electrochemical nitrogen reduction reaction (NRR) is a promising energy-efficient and low-emission alternative to the traditional Haber–Bosch process. Usually, the competing hydrogen evolution reaction (HER) and the reaction barrier of ambient electrochemical NRR are significant challenges, making a simultaneous high NH₃ formation rate and high Faradic efficiency (FE) difficult. To give effective NRR electrocatalysis and suppressed HER, the surface atomic structure of W₁₈O₄₉, which has exposed active W sites and weak binding for H₂, is doped with Fe. A high NH₃ formation rate of 24.7 μg h⁻¹ mg_cat⁻¹ and a high FE of 20.0 % are achieved at an overpotential of only −0.15 V versus the reversible hydrogen electrode. Ab initio calculations reveal an intercalation-type doping of Fe atoms in the tunnels of the W₁₈O₄₉ crystal structure, which increases the oxygen vacancies and exposes more W active sites, optimizes the nitrogen adsorption energy, and facilitates the electrocatalytic NRR.     

W/Mo-polyoxometalate-derived electrocatalyst for high-efficiency nitrogen fixation

Ammonia is the feedstock chemical for most fertilizers and the alternative of renewable energy carriers. Environmentally benign electrochemical nitrogen reduction reaction (NRR) under mild conditions has been recognized as one of the most attractive strategies for N₂ fixation. Herein, inspired by Mo-based nitrogenase, W/Mo-doping electrocatalysts were developed with mixed-metal polyoxometalate H₃PW₆Mo₆O₄₀ as the precursor for high performance electrocatalytic NRR. Trace amount of Pt was transplanted on the surface of W/Mo@rGO via in situ electroplating treatment to further improve the NRR performance. The resulting Pt-W/Mo@rGO-6 achieves excellent performance for NRR with a high NH₃ yield of 79.2 µg h^?1 mg_cat^?1 due to the multicomponent synergistic effect in the composite catalyst. The Pt-W/Mo@rGO-6 represents the first example of highly efficient NRR electraocatalyst derived from mixed-metal polyoxometalate, which exhibits outstanding stability confirmed by the constant catalytic performance over 24 h chronoamperometric test. This finding opens a new avenue to construct highly efficient NRR electrocatalyst by employing mixed metal polyoxometalate as the precursor under ambient conditions.     

Antimony‐Based Composites Loaded on Phosphorus‐Doped Carbon for Boosting Faradaic Efficiency of the Electrochemical Nitrogen Reduction Reaction

A nanocomposite of PC/Sb/SbPO₄ (PC, phosphorus‐doped carbon) exhibits a high activity and an excellent selectivity for efficient electrocatalytic conversion of N₂ to NH₃ in both acidic and neutral electrolytes under ambient conditions. At a low reductive potential of ?0.15 V versus the reversible hydrogen electrode (RHE), the PC/Sb/SbPO₄ catalyst achieves a high Faradaic efficiency (FE) of 31 % for ammonia production in 0.1 m HCl under mild conditions. In particular, a remarkably high FE value of 34 % is achieved at a lower reductive potential of ?0.1 V (vs. RHE) in a 0.1 m Na₂SO₄ solution, which is better than most reported electrocatalysts towards the nitrogen reduction reaction (NRR) in neutral electrolyte under mild conditions. The change in surface species and electrocatalytic performance before and after N₂ reduction is explored by an ex situ method. PC and SbPO₄ are both considered as the active species that enhanced the performance of NRR.     

Ambient Electrosynthesis of Ammonia on a Core–Shell-Structured Au@CeO2 Catalyst: Contribution of Oxygen Vacancies in CeO2

Electrosynthesis of NH₃ through the N₂ reduction reaction (NRR) under ambient conditions is regarded as promising technology to replace the industrial energy- and capital-intensive Haber–Bosch process. Herein, a room-temperature spontaneous redox approach to fabricate a core–shell-structured Au@CeO₂ composite, with Au nanoparticle sizes below about 10 nm and a loading amount of 3.6 wt %, is reported for the NRR. The results demonstrate that as-synthesized Au@CeO₂ possesses a surface area of 40.7 m² g⁻¹ and a porous structure. As an electrocatalyst, it exhibits high NRR activity, with an NH₃ yield rate of 28.2 μg h⁻¹ cm⁻² (10.6 μg h⁻¹ mg⁻¹_cat., 293.8 μg h⁻¹ mg⁻¹_Au) and a faradaic efficiency of 9.50 % at −0.4 V versus a reversible hydrogen electrode in 0.01 m H₂SO₄ electrolyte. The characterization results reveal the presence of rich oxygen vacancies in the CeO₂ nanoparticle shell of Au@CeO₂; these are favorable for N₂ adsorption and activation for the NRR. This has been further verified by theoretical calculations. The abundant oxygen vacancies in the CeO₂ nanoparticle shell, combined with the Au nanoparticle core of Au@CeO₂, are electrocatalytically active sites for the NRR, and thus, synergistically enhance the conversion of N₂ into NH₃.     

N2 Electroreduction to NH3 by Selenium Vacancy-Rich ReSe2 Catalysis at an Abrupt Interface

Vacancy engineering has been proved repeatedly as an adoptable strategy to boost electrocatalysis, while its poor selectivity restricts the usage in nitrogen reduction reaction (NRR) as overwhelming competition from hydrogen evolution reaction (HER). Revealed by density functional theory calculations, the selenium vacancy in ReSe₂ crystal can enhance its electroactivity for both NRR and HER by shifting the d-band from −4.42 to −4.19 eV. To restrict the HER, we report a novel method by burying selenium vacancy-rich ReSe₂@carbonized bacterial cellulose (V_r-ReSe₂@CBC) nanofibers between two CBC layers, leading to boosted Faradaic efficiency of 42.5 % and ammonia yield of 28.3 μg h⁻¹ cm⁻² at a potential of −0.25 V on an abrupt interface. As demonstrated by the nitrogen bubble adhesive force, superhydrophilic measurements, and COMSOL Multiphysics simulations, the hydrophobic and porous CBC layers can keep the internal V_r-ReSe₂@CBC nanofibers away from water coverage, leaving more unoccupied active sites for the N₂ reduction (especially for the potential determining step of proton-electron coupling and transferring processes as *NN → *NNH).     

Integrated Tandem Electrochemical-chemical-electrochemical Coupling of Biomass and Nitrate to Sustainable Alanine

Alanine is widely employed for synthesizing polymers, pharmaceuticals, and agrochemicals. Electrocatalytic coupling of biomass molecules and waste nitrate is attractive for the nitrate removal and alanine production under ambient conditions. However, the reaction efficiency is relatively low due to the activation of the stable substrates, and the coupling of two reactive intermediates remains challenging. Herein, we realize the integrated tandem electrochemical-chemical-electochemical synthesis of alanine from the biomass-derived pyruvic acid (PA) and waste nitrate (NO₃⁻) catalyzed by PdCu nano-bead-wires (PdCu NBWs). The overall reaction pathway is demonstrated as a multiple-step catalytic cascade process via coupling the reactive intermediates NH₂OH and PA on the catalyst surface. Interestingly, in this integrated tandem electrochemical-chemical-electrochemical catalytic cascade process, Cu facilitates the electrochemical reduction of nitrate to NH₂OH intermediates, which chemically couple with PA to form the pyruvic oxime, and Pd promotes the electrochemical reduction of pyruvic oxime to the desirable alanine. This work provides a green strategy to convert waste NO₃⁻ to wealth and enriches the substrate scope of renewable biomass feedstocks to produce high-value amino acids.     

Nanoporous Palladium Hydride for Electrocatalytic N2 Reduction under Ambient Conditions

The electrocatalytic nitrogen reduction reaction (NRR) is an alternative eco‐friendly strategy for sustainable N₂ fixation with renewable energy. However, NRR suffers from sluggish kinetics owing to difficult N₂ adsorption and N≡N cleavage. Now, nanoporous palladium hydride is reported as electrocatalyst for electrochemical N₂ reduction under ambient conditions, achieving a high ammonia yield rate of 20.4 μg h^?1 mg^?1 with a Faradaic efficiency of 43.6 % at low overpotential of 150 mV. Isotopic hydrogen labeling studies suggest the involvement of lattice hydrogen atoms in the hydride as active hydrogen source. In situ Raman analysis and density functional theory (DFT) calculations further reveal the reduction of energy barrier for the rate‐limiting *N₂H formation step. The unique protonation mode of palladium hydride would provide a new insight on designing efficient and robust electrocatalysts for nitrogen fixation.     

Tunable Periodically Ordered Mesoporosity in Palladium Membranes Enables Exceptional Enhancement of Intrinsic Electrocatalytic Activity for Formic Acid Oxidation

Developing superior electrocatalysts for formic acid oxidation (FAO) is the most crucial step in commercializing direct formic acid fuel cells. Herein, we electrodeposited palladium membranes with periodically ordered mesoporosity obtained by asymmetrically replicating the bicontinuous cubic phase structure of a lyotropic liquid‐crystal template. The Pd membrane with the largest periodicity and highest degree of order delivered up to 90.5 m² g^?1 of electrochemical active surface area and 3.34 A mg^?1 electrocatalysis capability towards FAO, 3.8 and 7.8 times the values of the commercial Pd/C catalyst, respectively. By controlling the temperature and potential of the electrodeposition procedure, the periodicity area and order degree of the mesoporosity are highly tunable. These Pd membranes gave prototype formic acid fueled cells with 4.3 and 2.4 times the maximum current and power density of the commercial Pd/C catalyst.     

Isolated Electron-Rich Ruthenium Atoms in Intermetallic Compounds for Boosting Electrochemical Nitric Oxide Reduction to Ammonia

The direct electrochemical nitric oxide reduction reaction (NORR) is an attractive technique for converting NO into NH₃ with low power consumption under ambient conditions. Optimizing the electronic structure of the active sites can greatly improve the performance of electrocatalysts. Herein, we prepare body-centered cubic RuGa intermetallic compounds (i.e., bcc RuGa IMCs) via a substrate-anchored thermal annealing method. The electrocatalyst exhibits a remarkable NH₄⁺ yield rate of 320.6 μmol h⁻¹ mg⁻¹_Ru with the corresponding Faradaic efficiency of 72.3 % at very low potential of −0.2 V vs. reversible hydrogen electrode (RHE) in neutral media. Theoretical calculations reveal that the electron-rich Ru atoms in bcc RuGa IMCs facilitate the adsorption and activation of *HNO intermediate. Hence, the energy barrier of the potential-determining step in NORR could be greatly reduced.