Crystal Facets Research Articles

Enhanced low-temperature CO oxidation activity through crystal facet engineering of Pd/CeO2 catalysts

Cerium dioxide (CeO2) supported palladium (Pd) catalysts have found widespread application in CO oxidation reaction owing to their exceptional catalytic performance. The morphology of the CeO2 support dictates the exposed crystal plane, exerting a profound influence on surface structure and redox properties. This is crucial as the atomic arrangement at the surface directly impacts catalytic activity. In this study, a range of CeO2 supports with diverse morphologies (e.g. nano-octahedra, nano-cubes, nano-particles, nano-spheres, and nano-rods) were successfully synthesized through hydrothermal methods and subsequently supported with Pd for CO oxidation. The spherical 1Pd/CeO2–S catalyst, revealing exposed (111) + (100) crystal planes, exhibited significantly higher CO catalytic oxidation activity compared to the catalysts with other morphological CeO2 supports. The results indicated a positive correlation between the content of PdxCe1-xO2-y species and catalytic activity. Notably, this species was most abundantly formed in the spherical 1Pd/CeO2–S catalyst with exposed (111) + (100) crystal planes. The presence of this active species facilitated the formation of surface defects, increased oxygen vacancy concentration, and enhanced metal-support interaction, consequently greatly improving the CO low-temperature catalytic oxidation activity. Consequently, the oxidation state of Pd in the Pd/CeO2 catalyst could be effectively regulated by controlling the exposure of (111) + (100) crystalline surfaces of the CeO2 support, further optimizing the catalytic performance of the Pd/CeO2 catalytic system.

PH-Dependent Morphology of Copper (II) Oxide in Hydrothermal Process and Their Photoelectrochemical Application for Non-Enzymatic Glucose Biosensor

In this study, we investigated the influence of pH on the hydrothermal synthesis of copper (II) oxide CuO nanostructures with the aim of tuning their morphology. By varying the pH of the reaction medium, we successfully produced CuO nanostructures with three distinct morphologies including nanoparticles, nanorods, and nanosheets according to the pH levels of 4, 7, and 12, respectively. The observed variations in surface morphology are attributed to fluctuations in growth rates across different crystal facets, which are influenced by the presence of intermediate species within the reaction. This report also compared the structural and optical properties of the synthesized CuO nanostructures and explored their potential for photoelectrochemical glucose sensing. Notably, CuO nanoparticles and nanorods displayed exceptional performance with calculated limits of detection of 0.69 nM and 0.61 nM, respectively. Both of these morphologies exhibited a linear response to glucose within their corresponding concentration ranges (3–20 nM and 20–150 nM). As a result, CuO nanorods appear to be a more favorable photoelectrochemical sensing method because of the large surface area as well as the lowest solution resistance in electroimpedance analysis compared to CuO nanoparticles and nanosheets forms. These findings strongly suggest the promising application of hydrothermal-synthesized CuO nanostructures for ultrasensitive photoelectrochemical glucose biosensors.

Preferred Crystallographic Orientation via Solution Bathing for High‐Performance Inverted Perovskite Photovoltaics

AbstractThe meticulous control of crystal facets in polycrystalline perovskite films offers valuable insights into the photoelectric properties, varying significantly with different orientations. Exploring effective means to regulate these facets is crucial, and further revealing the underlying mechanisms is needed. Here, the research employed green solution bathing to obtain high‐quality perovskite films with preferred crystallographic orientation. In brief, eco‐friendly 2‐pentanol is used as the solvent, and functional molecules 2‐(dimethylaminomethyl)‐4‐(2‐aminoethylthiomethyl)thiazole (DAT) are introduced into the solution bathing as the solute. By introducing DAT molecules, precise control over perovskite crystal nucleation kinetics is achieved, resulting in films with a preferential (100) facet orientation. Conversely, films without DAT exhibited distinct (111) facet orientation. The regulation of DAT on perovskite film crystal facet is verified through theoretical and crystallographic analyses. Theoretical calculations show that S atom of DAT binds most strongly to the (100) facet of FAPbI3, promoting surface energy reduction and thermodynamic enhancement, favoring (100) crystal orientation. Crystallographic characterization further proved the regulation effect. In addition, PL/TRPL tests confirm the regulation of DAT on superior photoelectric properties of (100)‐oriented perovskite films. The work introduces a novel approach and preparation process for regulating the crystal facets orientation of polycrystalline perovskite films.

Insight into material behavior via surface free energy calculations for common energetic materials

AbstractThe Gibbs Free energy is a driving force for equilibrium crystal shapes and the formation of crystal facets in molecular crystals. Orientation dependence of interfacial properties is linked to surface free energy (SFE). Prediction of orientation‐dependent properties such as thermal stability, mechanical response, and compatibility with binders require a systematic approach to the quantification of SFE. In molecular crystals, entropy has a much larger contribution among all ordered crystalline materials. In this paper, we extend our previously developed method to quantify SFE and entropy of β‐HMX to other common energetic materials–TATB, α‐RDX, and PETN. Two complimentary approaches, Nonequilibrium Thermodynamic Integration (NETI) and Steered Molecular Dynamics (SMD) methods are used to obtain insight into interfacial phenomena along with surface free energy estimates. We discuss the relevance of surface free energy and the importance of surface entropy for facetted molecular crystals in understanding crystal properties, activation of slip planes, and potential pathways for fracture. These values allow us to predict theoretical crystal shape using Wulff Construction, better understand the effect of hydrogen bonding on SFE, and the diversity of bonding environment in energetic crystals. In particular, in crystals with low stacking fault energy, the SMD values can be inconclusive due to the triggering of slip plane motions. In cases where SMD simulations lead to large deformations and high uncertainty, the NETI approach can still provide SFE estimates.

Crystal facet engineering of hollow cadmium sulfide for efficient photocatalytic hydrogen evolution

Metal sulfides have been considered as potential candidates for photocatalytic hydrogen production, but their practical applications are still limited by incident light utilization and charge separation despite the impressive advances in recent decades. To address these challenges, the construction of hollow nanostructure with exposing high active facets offers a desirable pathway for developing novel and high-efficiency photocatalysts. Here, by taking wurtzite CdS as an example, we first develop a general template-assisted cation exchange route for the preparation of hollow CdS nanostructures with diverse exposed facets. The obtained hollow CdS octahedrons with dominant {101} facets exhibit superior photocatalytic H2 evolution rate under visible-light irradiation compared with common CdS nanorods. According to the characterization results and density functional theory calculations, the excellent photocatalytic performance is attributed to the construction of hollow nano-octahedrons with exposed {101} active facets, which facilitates efficient light harvesting and photoinduced charge separation of CdS photocatalyst. The present approach gives a reference to design advanced semiconductors with remarkable photocatalytic activity for realizing efficient solar-to-chemical conversion.

Water Structure in the First Layers on TiO2: A Key Factor for Boosting Solar-Driven Water-Splitting Performances.

The water hydrogen-bonded network is strongly perturbed in the first layers in contact with the semiconductor surface. Even though this aspect influences the outer-sphere electron transfer, it was not recognized that it is a crucial factor impacting the solar-driven water-splitting performances. To fill this gap, we have selected two TiO2 anatase samples (with and without B-doping), and by extensive experimental and computational investigations, we have demonstrated that the remarkable 5-fold increase in water-splitting photoactivity of the B-doped sample cannot be ascribed to effects typically associated to enhanced photocatalytic properties, such as band gap, heterojunctions, crystal facets, and other aspects. Studying these samples by combining FTIR measurements under controlled humidity with first-principles simulations sheds light on the role and nature of the first-layer water structure in contact with the photocatalyst surfaces. It turns out that the doping hampers the percolation of tetrahedrally coordinated water molecules while enhancing the population of topological H-bond defects forming approximately linear H-bonded chains. This work unveils how doping the semiconductor surface affects the local electric field, determining the water splitting rate by influencing the H-bond topologies in the first water layers. This evidence opens new prospects for designing efficient photocatalysts for water splitting.

Boosting CO2 methanation activity by tuning Ni crystal plane and oxygen vacancy in Ni/CeO2 catalyst

It is challenging to boost CO2 methanation activity over Ni-based catalysts, and new findings that decipher the relationship between the essential laws of catalysts and their catalytic performance will be transformative. Herein, three kinds of Ni/CeO2 catalysts with different Ni crystal facets and oxygen vacancy are developed by varied preparation methods, which show significant differences in catalytic performance for CO2 methanation, and these catalysts are taken as a case study for the investigation of the crystal plane and oxygen vacancy effects in CO2 methanation as well. It is observed that the activity of Ni/CeO2-SG catalyst with abundant oxygen vacancies and principally exposed Ni (111) crystal facet is highly active for CO2 methanation reaction, which is 1–3 times than that of Ni/CeO2 catalysts with poor oxygen vacancy and/or Ni (111) crystal face. In addition, the former one cannot suffer from deactivation even in operation 130 h at 300 °C. Both structural investigations and catalytic evaluations indicate that the adsorption and activating ability of H2 and CO2 can be controlled by adjusting the Ni-exposed crystal face and oxygen vacancy concentration, respectively. It is also verified that the synergistic contribution of the Ni crystal facets and the oxygen vacancy play a crucial role in boosting the catalytic activity of the Ni/CeO2 catalysts by affecting the adsorption and activation of reactants. The Ni/CeO2 catalysts exposed Ni (111) crystal plane facilitate the catalytic activity by strengthing the H2 adsorption/dissociation capacity, while the abundantly available oxygen vacancies maximize the activity via acting as CO2 activation sites. Furthermore, the in situ DRIFT experiments reveal that the direct formate hydrogenation pathway is involved in the CO2 methanation process over the Ni/CeO2-SG catalyst.

Role of NiO in wide-bandgap perovskite solar cells based on self-assembled monolayers

NiO/self-assembled monolayer (SAM) double hole transport layers (HTLs) has become the mainstream choice in high-efficiency single-junction and tandem perovskite solar cells (PSCs). However, the underlying role of NiO in double HTLs from the microscale is not systematically revealed currently. Herein, we reveal that NiO plays an important role in inducing a more uniform and thinner SAM from three aspects. Firstly, compared with indium tin oxide (ITO), the NiO surface exposes less crystal facet orientations and a higher metal atom density, suggesting that sufficient chemical binding sites for SAMs are provided to facilitate the close-packed assembly of SAMs. Secondly, NiO modified ITO exhibits smaller surficial roughness and strongly bonded −OH, which is beneficial to the uniform distribution of SAMs and strong adhesion to the NiO surface. Utilizing the well-constructed SAM, we fabricate wide-bandgap (>1.75 eV) PSCs using vacuum-assisted technology and achieve an impressive photoelectric conversion efficiency of 19.55 %. These findings not only deepen the understanding of SAM assembly on substrates but also provide essential guidance for the future industrialization of PSCs.

The influence of crystal facet on the catalytic performance of MOFs-derived NiO with different morphologies for the total oxidation of propane: The defect engineering dominated by solvent regulation effect

Crystal facet and defect engineering are crucial for designing heterogeneous catalysts. In this study, different solvents were utilized to generate NiO with distinct shapes (hexagonal layers, rods, and spheres) using nickel-based metal-organic frameworks (MOFs) as precursors. It was shown that the exposed crystal facets of NiO with different morphologies differed from each other. Various characterization techniques and density functional theory (DFT) calculations revealed that hexagonal-layered NiO (NiO-L) possessed excellent low-temperature reducibility and oxygen migration ability. The (111) crystal plane of NiO-L contained more lattice defects and oxygen vacancies, resulting in enhanced propane oxidation due to its highest O2 adsorption energy. Furthermore, the higher the surface active oxygen species and surface oxygen vacancy concentrations, the lower the C−H activation energy of the NiO catalyst and hence the better the catalytic activity for the oxidation of propane. Consequently, NiO-L exhibited remarkable catalytic activity and good stability for propane oxidation. This study provided a simple strategy for controlling NiO crystal facets, and demonstrated that the oxygen defects could be more easily formed on NiO(111) facets, thus would be beneficial for the activation of C−H bonds in propane. In addition, the results of this work can be extended to the other fields, such as propane oxidation to propene, fuel cells, and photocatalysis.

Oriented construction between crystal facet homojunction and S vacancies on CdS for boosting photocatalytic H2 evolution

Though the different exposed crystal facets of cadmium sulfide (CdS) catalysts have been demonstrated to enhance their photocatalytic activity, the mechanism behind H2 evolution on these diverse facets remains elusive. Here, we synthesized CdS photocatalysts with co-exposed (101) and (002) crystal facets, incorporating S vacancies via a hydrothermal method within the temperature range from 80 to 240 °C. The resulting CdS nanorods exhibited exposed (002) and (101) crystal facets, demonstrating abundant S vacancies, and showcased a notable photocatalytic hydrogen (H2) evolution activity of 467.67 μmol g−1·h−1—approximately 144 times higher than that of CdS nanoparticles. Both experimental results and density functional theory (DFT) calculations showed the significance of co-exposed (101) and (002) crystal facets as self-constructed crystal homojunctions on CdS, facilitating efficient spatial separation of photogenerated charges. Additionally, co-exposed (101) and (002) crystal facets with S vacancies, stemming from the mismatched lattice, were observed to enhance the adsorption of water (H2O) molecules. This, in turn, reduced the energy required for H2 dissociative adsorption, providing thermodynamic advantages. The understanding of the synergistic effect between self-constructed (101) and (002) facet junctions and S vacancies on CdS for boosting photocatalytic H2 evolution holds promise for expanding the applications of CdS-based materials in various photocatalytic processes.

Crystal Facet Control of Nickel–Cobalt Sulfide Nanostructure and Study of Supercapacitor Performance

Supercapacitors require excellent cycling stability and rate capability for electrodes. The NiCo2S4 spinel structure has caught much attention for its high conductivity and high theoretical specific capacity. However, due to the lack of active sites, it has been restricted in supercapacitors. In this research, the NiCo2S4 nano-material with needle, sheet and porous network morphologies were prepared by the addition of different kinds of surfactants via a simple hydrothermal method. At 1[Formula: see text]mA/cm2, capacitance of these NiCo2S4 nanomaterials is measured as 2.09[Formula: see text]F/cm2, 3.22[Formula: see text]F/cm2, and 4.42[Formula: see text]F/cm2, respectively. It was found that the exposure ratio of (111) and (220) crystal facets also has an effect on electrochemical performance, and NiCo2S4 with I[Formula: see text]/I[Formula: see text] of 3:1 showed better performance. Furthermore, NiCo2S4-PN//AC asymmetrical supercapacitor was assembled with NiCo2S4-PN serving as positive electrode and activated carbon (AC) as negative electrode. At a power density of 7.284[Formula: see text]mW/cm2, energy density achieved was 0.625[Formula: see text]mWh/cm2. Additionally, capacitance retention rate remained at 79.6% of initial capacitance after 1500 cycles. These outcomes are of great significance for developing more efficient, stable and reliable transition metal sulfide-based supercapacitors.

PH-dependent growth of alumina nanorods with a high aspect ratio for enhanced propane dehydrogenation performance

Controllable synthesis of porous alumina is always challenging due to the diversity of precursors and the complexity of the growth process. In this work, alumina nanorods with adjustable aspect ratios were synthesized by precipitation to investigate the morphology evolution mechanism related to aging pH, and the structure–activity relationship of alumina. The evolution path of precursors ammonium aluminum carbonate hydroxide (NH4Al(OH)2CO3, AACH) was established by tracking the variation in electrical charges and nitrate concentration during the growth process. It was revealed that the anisotropic adsorption of ions on the AACH crystal facets can modulate the axial and radial growth rates of the microcrystalline rods, regulating the one-dimensional oriented assembly of AACH. Alumina synthesized at pH 9.5 exhibited more exposition of (100) facets due to its higher aspect ratio, resulting in an aluminum content of up to 30% in the five-coordinated state. Due to the presence of strong metal-support interactions, the corresponding PtSn/Al2O3 catalyst demonstrated good propane dehydrogenation activity and stability, with propylene formation with 99% selectivity within 30 h of reaction. This study highlighted the significance of pH regulation in the growth environment of AACH, enabling the selective exposure of crystal facets in the alumina support, and providing an effective pathway to obtain highly active and stable catalysts.

Elucidating Facet-Dependent Photocatalytic Activities of Metastable CdS and Au@CdS Core-Shell Nanocrystals.

Controlling the crystal facets of semiconductor nanocrystals (NCs) has been proven as an effective approach to tune their physicochemical properties. However, the study on facet-engineering of metastable zinc blende CdS (zb-CdS) and its heterostructures is still not fully explored. In this study, the zb-CdS and Au@zb-CdS core-shell NCs with tunable terminating facets are controllably synthesized, and their photocatalytic performance for water splitting are evaluated. It is found that the {111} facets of the zb-CdS NCs display higher intrinsic activity than the {100} counterparts, which originates from these surfaces being much more efficient, facilitating electron transition to enhance the adsorption ability and the dissociation of the adsorbed water, as revealed by theoretical calculations. Moreover, the Au@zb-CdS core-shell NCs exhibit better photocatalytic performance than the zb-CdS NCs terminated with the same facets under visible light irradiation (≥400 nm), which is mainly ascribed to the accelerated electron separation at the interface, as demonstrated by femtosecond transient absorption (fs-TA) spectroscopy. Importantly, the quantum yield of plasmon-induced hot electron transfer quantified by fs-TA in the Au@zb-CdS core-shell octahedrons can be reached as high as 1.2% under 615 nm excitation, which is higher than that of the Au@zb-CdS core-shell cubes. This work unravels the face-dependent photocatalytic performance of the metastable semiconductor NCs via a combination of experiments and theoretical calculations, providing the understanding of the underlying mechanism of these photocatalysts.

How Does Nodular Chromite Nucleate and Grow? An Integrated Microstructural and Petrological Approach

Abstract Nodular chromite ore deposits are found in ophiolites and crop out in structures interpreted as former dykes. Most of them are transposed parallel to the plastic foliation of the host peridotite. Many studies have been conducted in order to decipher the origin and evolution of nodular chromite but the outstanding lack of consensus paves the way for an integrated field, geochemical and microstructural approach to be carried out. We sampled the well-characterized Maqsad chromitite dyke that crops out at the top of the mantle–crust dunitic transition zone in the Oman ophiolite and that was not affected by transposition. The spectacular variations in nodule size and texture and their distribution within the dyke have been perfectly preserved which is a rather unique situation. We selected about 40 nodules representative of the shapes and size variability of this ore deposit. Nodules have been classified in three categories: Type-1 nodules are large skeletal chromite grains associated with amphibole and olivine filling their former porosity; Type-3 nodules have a central nucleus of chromite/silicate surrounded by a mantle of close-packed chromite grains. Their shape is best described as almond-like, and they may reach 3 cm in length; Type-2 includes all of the intermediate nodules shapes and sizes between type-1 and type-3 varieties. Electron Probe MicroAnalyser (EPMA) transects and maps show that mineral chemical variations in type-1 nodules and in the nuclei of type-2 and type-3 nodules record out of equilibrium crystal growth. They exhibit high XCr and relatively low-TiO2 and likely resulted from transient interactions between hydrothermal fluids and basaltic melts. Contrary to type-1 and nuclei, the mantles of type-2 and -3 nodules have lower Cr2O3 contents, decreasing toward the nodule edges. They are richer in TiO2 than type-1 nodules but concentration patterns of this element along edge to edge transects are quite variable. The chromite mantles of type-2 and -3 are best understood as the fractional crystallization products of a parent melt of type-1 nodules in different pFluids and/or redox conditions. The analysis of the distribution of the misorientation axis between the skeletal grains and the adjacent chromite grains in the mantle (N = 222 in 28 nodules) revealed a clustering around a [111] axis across the whole range of misorientation angles. Accordingly, we suggest that the growth of the Maqsad nodules is achieved by accretion of finer euhedral chromite grains onto a skeletal chromite grain by juxtaposition of their flat crystal facets. Combined EDS-EBSD mapping together with EPMA transects revealed that a ~1-mm-thick rim of high XCr, displaying a homothetic shape to its corresponding nuclei, is a common feature in the mantle when the nodule sizes exceed about 1 cm. We interpret this observation as the result of the accretion of grains with higher XCr compositions during the nodule construction. Overall, our new study of the Maqsad nodular chromitite highlights the peculiar and transient conditions needed to give rise to the textural and chemical complexity that is preserved in these enigmatic rocks.

Local-strain-induced CO2 adsorption geometries and electrochemical reduction pathway shift

ABSTRACT Unravelling the influence of strain and geometric effects on the electrochemical reduction of carbon dioxide (CO2RR) on Cu-based (or Pd-based) alloys remains challenging due to complex local microenvironment variables. Herein, we employ two PdCu alloys (nanoparticles and nanodendrites) to demonstrate how CO2RR selectivity can shift from CO to HCOO−. Despite sharing consistent phases, exposed crystal facets, and overall oxidative states, these alloys exhibit different local strain profiles due to their distinct geometries. By integrating experimental data, in-situ spectroscopy, and density functional theory calculations, we revealed that CO2 prefers adsorption on tensile-strained areas with carbon-side geometry, following a *COOH-to-CO pathway. Conversely, on some compressive-strained regions induced by the dendrite-like morphology, CO2 adopts an oxygen-side geometry, favoring an *OCHO-to-HCOO pathway due to the downshift of the d-band center. Notably, our findings elucidate a dominant *OCHO-to-HCOO− pathway in catalysts when featuring both adsorption geometries. This research provides a comprehensive model for local environment of bimetallic alloys, and establishes a clear relationship between the CO2RR pathway shift and variation in local strain environments of PdCu alloys.

Reduced graphene oxide encapsulated octahedral NiSe2 nanocrystals with dominant {111} crystal facets for efficient hydrogen evolution reaction

Regulating the exposed crystal facets of electrocatalysts is an effective means to enhance their electrocatalytic activity. However, related studies have focused mainly on traditional noble metals or metal oxides based electrocatalysts, while the research on crystal facets dependent electrocatalytic activity of metal selenides is still very rare. Here, crystal facets effect of cubic NiSe2 in electrocatalytic HER was studied. It was shown that octahedral NiSe2 nanocrystals dominated by active {111} crystal facets exhibited significantly enhanced HER activity. Moreover, by encapsulating the octahedral NiSe2 nanocrystals into reduced graphene oxide (rGO) nanosheet networks, further improvement in their HER activity could be achieved. First principles calculations and experimental characterization indicated that {111} crystal facts of NiSe2 had abundant surface active sites and ideal catalytic reaction energy barriers. This study not only expands the research on crystal facets-dependent HER activity, but also gains a deep understanding of the electrocatalytic mechanism.

Enhancement of H2O2 generation rate in porphyrin photocatalysts via crystal facets regulation to create strong internal electric field

Enhancement of H2O2 generation rate in porphyrin photocatalysts via crystal facets regulation to create strong internal electric field

Ultrathin 2D Alloyed Cu−Ga−Zn−S Curved Nanobelts for Boosting Visible‐Light Photocatalytic Hydrogen Evolution

Abstract2D semiconductor nanomaterials have received significant attention as photocatalysts for solar‐to‐hydrogen conversion due to their robust light absorption capacity, large specific surface area, and superior electron transport characteristics. Nevertheless, it is challenging to develop 2D quaternary copper‐based sulfides (QCSs) with functional integration of conducive structural features for photocatalysis from multiple elements and intricate control conditions. Herein, ultrathin 2D alloyed Cu−Ga−Zn−S (CGZS) curved nanobelts (NBs) are fabricated by using a facile one‐pot colloidal method. Subsequently, the derived Cu31S16‐CGZS Janus heterostructures are designed by increasing Cu concentrations. The formation mechanism of 2D curved alloys and Janus heterostructures is systematically investigated. Without cocatalysts, curved alloyed CGZS NBs demonstrated superior photocatalytic activities of 1264.2 µmol g−1 h−1 compared to Janus heterostructured Cu31S16−CGZS (463.1 µmol g−1 h−1) under visible light (> 400 nm). Experimental and theoretical results unveiled that the improved photocatalytic activities of curved CGZS NBs can be attributed to enhanced charge–carrier separation efficiency resulting from high crystallinity and ultrathin 2D structure, abundant active sites from curved structure, high‐active (0001) crystal facet with the lowest reaction Gibbs energy, work function, and metal‐like properties. This work offers new insights into functional integration into ultrathin 2D QCSs with enhanced visible‐light photocatalytic performance.

Electrochemical Nitrate Reduction to Ammonia on CuCo Nanowires at Practical Level

AbstractElectrochemical reduction of nitrate (NO3RR) holds great promise for environmentally friendly ammonia production. Tandem catalysis is a promising strategy for boosting the NO3RR and inhibiting side effects, but it is still challenged by lacking well‐designed catalysts to drive this catalytic process. Herein, the study develops the CuCo branched nanowires (CuCo NW) catalyst, which efficiently converts NO3 − to NH3 on Co (111) and Cu (111) crystal facets through a tandem catalysis mechanism. The in situ grown CuCo NW on Cu foam demonstrates a remarkable Faraday efficiency of 90.3% at 1.0 A cm−2 and maintains stable operation for 200 h at 100 and 200 mA cm−2 in a flow reactor. Density functional theory calculations suggest that the initial absorption and subsequent deoxygenation of *NO3 on Co (111) leading to the formation of *NO2, followed by its transfer to Cu (111) and further conversion to *NH3, establish an optimal pathway by managing rate‐determining steps on individual surfaces for NO3RR. To showcase the practical application of the catalyst, the study further develops a scaling‐up prototype reactor for continuous ammonia production, realizing the gram‐level yield rate of 1474.09 mg h−1 and Faraday efficiency of 91.26% at practical‐level 20.0 A.

Sub-2.5 nm monodisperse Mo2C nanoparticles on N-doped carbon: The facet engineering for boosting electrochemical hydrogen evolution

Molybdenum carbide materials have demonstrated remarkable potential in catalyzing the hydrogen evolution reaction (HER). However, further modulation of their performance through simultaneously engineering the size and surface crystal facets remains challenging. Herein, we report the successful fabrication of N-doped carbon-supported monodisperse Mo2C nanoparticles with a size of ∼2.06 nm, exhibiting co-exposed (101)/(102) facets-heterojunction, derived from annealing glycine and ammonium molybdate tetrahydrate. The optimized Mo2C/NC-Amt catalyst exhibits a low overpotentials of 128 mV to achieve the current density of 10 mA cm−2 and a small Tafel slope of 72 mV dec−1 under alkaline solution. By changing the molybdate precursor, the phase and crystal facet composition of molybdenum carbide can be effectively tuned, which provides a good platform for studying their structure-activity in HER. The theoretical calculations reveal the synergistic effect of (101)/(102) facets-heterojunction accelerates electron transfer and regulates the d band center of Mo2C, reducing the reaction barriers of intermediates in the HER process, thus significantly boosting reaction activity. This work proposes a novel insight into the rational fabrication of efficient HER catalysts through facet engineering toward heterojunction construction under the 2.5 nm region.