CeNCl-CeO2 Heterojunction-Modified Ni Catalysts for Efficient Electroreduction of CO2 to CO

Renewable-electricity-powered electrochemical CO₂ reduction (CO₂RR) is considered one of the most promising ways to convert exhaust CO₂ into value-added chemicals and fuels. Among various CO₂RR products, CO is of great significance since it can be directly used as feedstock to produce chemical products through the Fischer–Tropsch process. However, the CO₂-to-CO electrocatalytic process is often accompanied by a kinetically competing side reaction: H₂ evolution reaction (HER). Designing electrocatalysts with tunable electronic structures is an attractive strategy to enhance CO selectivity. In this work, a CeNCl-CeO₂ heterojunction-modified Ni catalyst is successfully synthesized with high CO₂RR catalytic performance by the impregnation-calcination method. Benefiting from the strong electron interaction between the CeNCl-CeO₂ heterojunction and Ni nanoparticles (NPs), the catalytic performance is greatly improved. Maximal CO Faradaic efficiency (FE) is up to 90% at −0.8 V (vs RHE), plus good stability close to 12 h. Detailed electrochemical tests and density functional theory (DFT) calculation results reveal that the introduction of the CeNCl-CeO₂ heterojunction tunes the electronic structure of Ni NPs. The positively charged Ni center leads to an enhanced local electronic structure, thus promoting the activation of CO₂ and the adsorption of ^*COOH.     

Simultaneous Achieving of High Faradaic Efficiency and CO Partial Current Density for CO2 Reduction via Robust,Noble‐Metal‐Free Zn Nanosheets with Favorable Adsorption Energy

Electrocatalytic CO₂ reduction to fuels is considered a promising strategy for the sustainable carbon cycle. However, the improvement of the catalytic performance of CO₂ electrocatalysts still poses many challenges, especially achieving the large partial current density of product and high faradaic efficiency simultaneously, which are essential for future applications of the electrochemical CO₂ reduction reaction. In response, herein, an in situ porous Zn catalyst is prepared and exhibits high faradaic efficiency and large CO partial current density at the same time, benefiting from the porous architecture with increased exposure and accessibility of active sites. Furthermore, density functional theory calculations demonstrate that the high faradaic efficiency is attributed to the favorable adsorption energy of the key intermediate, which promotes CO₂ electroreduction to CO.     

Shape‐Controlled CO2 Electrochemical Reduction on Nanosized Pd Hydride Cubes and Octahedra

Electrochemical CO₂ reduction reaction (CO₂RR) provides a potential pathway to mitigate challenges related to CO₂ emissions. Pd nanoparticles have shown interesting properties as CO₂RR electrocatalysts, while how different facets of Pd affect its performance in CO₂ reduction to synthesis gas with controlled H₂ to CO ratios has not been understood. Herein, nanosized Pd cubes and octahedra particles dominated by Pd(100) and Pd(111) facets are, respectively, synthesized. The Pd octahedra particles show higher CO selectivity (up to 95%) and better activity than Pd cubes and commercial particles. For both Pd octahedra and cubes, the ratio of H₂/CO products is tunable between 1 and 2, a desirable ratio for methanol synthesis and the Fischer–Tropsch processes. Further studies of Pd octahedra in a 25 cm² flow cell show that a total CO current of 5.47 A is achieved at a potential of 3.4 V, corresponding to a CO partial current density of 220 mA cm^?2. In situ X‐ray absorption spectroscopy studies show that regardless of facet Pd is transformed into Pd hydride (PdH) under reaction conditions. Density functional theory calculations show that the reduced binding energies of CO and HOCO intermediates on PdH(111) are key parameters to the high current density and Faradaic efficiency in CO₂ to CO conversion.     

Activation of Ni Particles into Single Ni–N Atoms for Efficient Electrochemical Reduction of CO2

Electrochemical reduction of carbon dioxide (CO₂) to fuels and value‐added industrial chemicals is a promising strategy for keeping a healthy balance between energy supply and net carbon emissions. Here, the facile transformation of residual Ni particle catalysts in carbon nanotubes into thermally stable single Ni atoms with a possible NiN₃ moiety is reported, surrounded with a porous N‐doped carbon sheath through a one‐step nanoconfined pyrolysis strategy. These structural changes are confirmed by X‐ray absorption fine structure analysis and density functional theory (DFT) calculations. The dispersed Ni single atoms facilitate highly efficient electrocatalytic CO₂ reduction at low overpotentials to yield CO, providing a CO faradaic efficiency exceeding 90%, turnover frequency approaching 12 000 h^?1, and metal mass activity reaching about 10 600 mA mg^?1, outperforming current state‐of‐the‐art single atom catalysts for CO₂ reduction to CO. DFT calculations suggest that the Ni@N₃ (pyrrolic) site favors *COOH formation with lower free energy than Ni@N₄, in addition to exothermic CO desorption, hence enhancing electrocatalytic CO₂ conversion. This finding provides a simple, scalable, and promising route for the preparation of low‐cost, abundant, and highly active single atom catalysts, benefiting future practical CO₂ electrolysis.     

Nanoporous Au Thin Films on Si Photoelectrodes for Selective and Efficient Photoelectrochemical CO2 Reduction

An Si photoelectrode with a nanoporous Au thin film for highly selective and efficient photoelectrochemical (PEC) CO₂ reduction reaction (CO₂RR) is presented. The nanoporous Au thin film is formed by electrochemical reduction of an anodized Au thin film. The electrochemical treatments of the Au thin film critically improve CO₂ reduction catalytic activity of Au catalysts and exhibit CO Faradaic efficiency of 96% at 480 mV of overpotential. To apply the electrochemical pretreatment of Au films for PEC CO₂RR, a new Si photoelectrode design with mesh‐type co‐catalysts independently wired at the front and the back of the photoelectrode is demonstrated. Due to the superior CO₂RR activity of the nanoporous Au mesh and high photovoltage from Si, the Si photoelectrode with the nanoporous Au thin film mesh shows conversion of CO₂ to CO with 91% Faradaic efficiency at positive potential than the CO₂/CO equilibrium potential.     

2D Assembly of Confined Space toward Enhanced CO2 Electroreduction

Rational design of electrocatalysts toward efficient CO₂ electroreduction has the potential to reduce carbon emission and produce value‐added chemicals. In this work, a strategy of constructing 2D confined‐space as molecular reactors for enhanced electrocatalytic CO₂ reduction selectivity is demonstrated. Highly ordered 2D nanosheet lamella assemblies are achieved via weak molecular interaction of atomically thin titania nanosheets, a variety of cationic surfactants, and SnO₂ nanoparticles. The interlayer spacings can be tuned from 0.9 to 3.0 nm by using different surfactant molecules. These 2D assemblies of confined‐space catalysts exhibit a strong size dependence of CO₂ electroreduction selectivity, with a peak Faradaic efficiency of 73% for formate production and excellent electrochemical stability at an optimal interspacing of ≈2.0 nm. This work suggests great potential for constructing new molecular‐size reactors, for highly selective electrocatalytic CO₂ reduction.     

Predicting CO2 adsorption and reactivity on transition metal surfaces using popular density functional theory methods

ABSTRACT

In this work, with Ni (110) as a model catalyst surface and CO₂ as an adsorbate, a performance study of Density Functional Theory methods (functionals) is performed. CO being a possible intermediate in CO₂ conversion reactions, binding energies of both, CO₂ and CO, are calculated on the Ni surface and are compared with experimental data. OptPBE-vdW functional correctly predicts CO₂ binding energy on Ni (?62?kJ/mol), whereas CO binding energy is correctly predicted by the rPBE-vdW functional (?138?kJ/mol). The difference in computed adsorption energies by different functionals is attributed to the calculation of gas phase CO₂. Three alternate reaction systems based on a different number of C=O double bonds present in the gas phase molecule are considered to replace CO₂. The error in computed adsorption energy is directly proportional to the number of C=O double bonds present in the gas phase molecule. Additionally, both functionals predict similar carbon–oxygen activation barrier (40?kJ/mol) and equivalent C1s shifts for probe species (?2.6?eV for CCH₃ and +1.5?eV CO₃^?), with respect to adsorbed CO₂. Thus, by including a correction factor of 28?kJ/mol for the computed CO₂ gas phase energy, we suggest using rPBE-vdW functional to investigate CO₂ conversion reactions on different metals.     

In-Situ Constructuring of Copper-Doped Bismuth Catalyst for Highly Efficient CO2 Electrolysis to Formate in Ampere-Level

CO₂ electrochemical reduction (CO₂RR) can mitigate environmental issues while providing valuable products, yet challenging in activity, selectivity, and stability. Here, a CuS-Bi₂S₃ heterojunction precursor is reported that can in situ reconstruct to Cu-doped Bismuth (CDB) electrocatalyst during CO₂RR. The CDB exhibits an industrial-compatible current density of −1.1 A cm⁻² and a record-high formate formation rate of 21.0 mmol h⁻¹ cm⁻² at −0.86 V versus the reversible hydrogen electrode toward CO₂RR to formate, dramatically outperforming currently reported catalysts. Importantly, the ultrawide potential region of 1050 mV with high formate Faradaic efficiency of over 90% and superior long-term stability for more than 100 h at −400 mA cm⁻² can also be realized. Experimental and theoretical studies reveal that the remarkable CO₂RR performance of CDB results from the doping effect of Cu which optimizes adsorption of the *OCHO and boosts the structural stability of metallic bismuth catalyst. This study provides valuable inspiration for the design of element-doping electrocatalysts to enhance catalytic activity and durability.     

Bi‐Based Metal‐Organic Framework Derived Leafy Bismuth Nanosheets for Carbon Dioxide Electroreduction

Electroreduction of carbon dioxide (CO₂) into high‐value and readily collectable liquid products is vital but remains a substantial challenge due to the lack of highly efficient and robust electrocatalysts. Herein, Bi‐based metal‐organic framework (CAU‐17) derived leafy bismuth nanosheets with a hybrid Bi/Bi? O interface (Bi NSs) is developed, which enables CO₂ reduction to formic acid (HCOOH) with high activity, selectivity, and stability. Specially, the flow cell configuration is employed to eliminate the diffusion effect of CO₂ molecules and simultaneously achieve considerable current density (200 mA cm^?2) for industrial application. The faradaic efficiency for transforming CO₂ to HCOOH can achieve over 85 or 90% in 1 m KHCO₃ or KOH for at least 10 h despite a current density that exceeds 200 mA cm^?2, outperforming most of the reported CO₂ electroreduction catalysts. The hybrid Bi/Bi? O surface of leafy bismuth nanosheets boosts the adsorption of CO₂ and protects the surface structure of the as‐prepared leafy bismuth nanosheets, which benefits its activity and stability for CO₂ electroreduction. This work shows that modifying electrocatalysts by surface oxygen groups is a promising pathway to regulate the activity and stability for selective CO₂ reduction to HCOOH.     

Dramatically Enhanced Ambient Ammonia Electrosynthesis Performance by In‐Operando Created Li–S Interactions on MoS2 Electrocatalyst

The Haber‐Bosch process can be replaced by the ambient electrocatalytic N₂ reduction reaction (NRR) to produce NH₃ if suitable electrocatalysts can be developed. However, to develop high performance N₂ fixation electrocatalysts, a key issue to be resolved is to achieve efficient hydrogenation of N₂ without interference by the thermodynamically favored hydrogen evolution reaction (HER). Herein, in‐operando created strong Li–S interactions are reported to empower the S‐rich MoS₂ nanosheets with superior NRR catalytic activity and HER suppression ability. The Li⁺ interactions with S‐edge sites of MoS₂ can effectively suppress hydrogen evolution reaction by reducing H* adsorption free energy from 0.03 to 0.47 eV, facilitate N₂ adsorption by increasing N₂ adsorption free energy from –0.32 to –0.70 eV and enhance electrocatalytic N₂ reduction activity by decreasing the activation energy barrier of the reaction control step (*N₂ → *N₂H) from 0.84 to 0.42 eV. A NH₃ yield rate of 43.4 μg h^?1 mg^?1 MoS₂ with a faradaic efficiency (FE) of 9.81% can be achieved in presence of strong Li–S interactions, more than 8 and 18 times by the same electrocatalyst in the absence of Li–S interactions. This report opens a new way to design and develop catalysts and catalysis systems.     

Electrochemical CO2 Reduction with Atomic Iron‐Dispersed on Nitrogen‐Doped Graphene

Electrochemical reduction of CO₂ provides an opportunity to reach a carbon‐neutral energy recycling regime, in which CO₂ emissions from fuel use are collected and converted back to fuels. The reduction of CO₂ to CO is the first step toward the synthesis of more complex carbon‐based fuels and chemicals. Therefore, understanding this step is crucial for the development of high‐performance electrocatalyst for CO₂ conversion to higher order products such as hydrocarbons. Here, atomic iron dispersed on nitrogen‐doped graphene (Fe/NG) is synthesized as an efficient electrocatalyst for CO₂ reduction to CO. Fe/NG has a low reduction overpotential with high Faradic efficiency up to 80%. The existence of nitrogen‐confined atomic Fe moieties on the nitrogen‐doped graphene layer is confirmed by aberration‐corrected high‐angle annular dark‐field scanning transmission electron microscopy and X‐ray absorption fine structure analysis. The Fe/NG catalysts provide an ideal platform for comparative studies of the effect of the catalytic center on the electrocatalytic performance. The CO₂ reduction reaction mechanism on atomic Fe surrounded by four N atoms (Fe–N₄) embedded in nitrogen‐doped graphene is further investigated through density functional theory calculations, revealing a possible promotional effect of nitrogen doping on graphene.     

Distinctive Supercapacitive Properties of Copper and Copper Oxide Nanocrystals Sharing a Similar Colloidal Synthetic Route

CuO and Cu₂O are non‐noble transition metal oxide supercapacitive materials with high theoretical specific capacitances above 1800 F g^?1. In this work, by adjusting organic additives of a colloidal system, Cu, Cu₂O, and CuO are grown in situ on nickel foam. CuO exhibits a specific capacitance of 1355 F g^?1 at 2 A g^?1 in 3 m KOH, a value well above those of Cu and Cu₂O (<500 F g^?1), and is superior to other known CuO electrodes. The CuO electrode exhibits 70% of its initial capacity, and the Columbic efficiency remains ≈100% after 7000 cycles at 4 A g^?1. Cu₂O exhibits the worst electrochemical performance, mainly due to the inactive barrier layer forming on the surface. This work provides an efficient synthetic platform for both comparable supercapacitive studies and cost‐effective electrochemical energy storage applications.     

Manganese Oxide Modified Nickel Catalysts for Photothermal CO Hydrogenation to Light Olefins

Ni‐based catalysts are traditionally considered unsuitable for the Fischer–Tropsch syntheses of olefins, due to the very strong hydrogenation ability of metallic Ni. Herein, this paradigm is challenged. A series of MnO supports nickel catalysts (denoted herein as Ni‐x) are fabricated by H₂ reduction of a nickel‐manganese mixed metal oxide at temperatures (x) ranging from 250 to 600 °C. The Ni‐500 catalyst displays unprecedented performance for photothermal CO hydrogenation to olefins, with an olefin selectivity of 33.0% under ultraviolet–visible irradiation. High‐resolution transmission electron microscopy, X‐ray absorption spectroscopy (XAS), and X‐ray diffraction analyses reveal that the Ni‐x catalysts contain metallic Ni nanoparticles supported by MnO. X‐ray photoelectron spectroscopy and XAS establish that electron transfer from MnO to the Ni⁰ nanoparticles is responsible for modifying the electronic structure of nickel (creating Ni^δ? states), thereby shifting the CO hydrogenation selectivity toward light olefins. Further, density functional theory calculations show that this electron transfer lowers the adsorption energies of olefins on Ni surfaces, thus minimizing the undesirable deep hydrogenation reactions to higher alkanes. This study conclusively demonstrates that MnO‐modified Ni‐based catalyst systems can be highly selective for CO hydrogenation to light olefins.     

Mechanistic insight into effect of doping of Ni on CO<Subscript>2</Subscript> reduction on the (111) facet of Cu: thermodynamic and kinetic analyses of the elementary steps

A systematic mechanistic investigation of CO₂ reduction on a Ni-modified Cu(111) surface is performed based on an extensive set of density functional theory (DFT) calculations by focusing on the hydrocarbon CH₄ formation pathways. By carefully analyzing reduction pathways on the Ni-modified Cu(111) surface, some important mechanistic information is deduced. The presence of Ni stabilizes all reaction intermediates, and thus reduces the activation barrier for almost all CO₂ reduction steps. Most importantly, it can considerably lower than the activation barrier of CO₂ hydrogenative dissociation into CO, which is the rate-determining step of CO₂ reduction on a pure Cu(111) surface. Thus, the doping of Ni atom is able to activate CO₂, leading to enhanced surface activity of CO₂ reduction into hydrocarbons. Notably, the activation barriers that are required for CH₄ and CH₃OH formation are almost all easily overcome through the thermoactive process at ambient temperatures after doping of Ni atom. Thus, a higher CH₄ and CH₃OH yield may be expected in the presence of the doped Ni atom. Thermodynamic analyses indicate that doping of Ni may reduce the overpotential of CO formation through CO₂ hydrogenative dissociation. On this basis, two decriptors may be proposed in order to describe the catalytic activity of Cu-based catalysts for CO₂ reduction, and a perfect Cu-based alloy in CO₂ reduction should moderately bind CO and form and reduce CO more easily. Simutaneously, CO hydrogenation occurs more easily on the (111) facet of Ni-modified Cu than dimerization, thereby the selectivity of (111) facet of Cu on production CH₄ is further confirmed to some degree. The present study reveals a rich reaction chemistry and provides new insights to guide the rational design of Cu-based alloy catalysts for hydrocarbons formation from CO₂ reduction.

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Graphical Abstract Reduction pathways of CO₂ into hydrocarbons?

     

Elucidating the Sole Contribution from Electromagnetic Near‐Fields in Plasmon‐Enhanced Cu2O Photocathodes

Despite many promising reports of plasmon‐enhanced photocatalysis, the inability to identify the individual contributions from multiple enhancement mechanisms has delayed the development of general design rules for engineering efficient plasmonic photocatalysts. Herein, a plasmonic photocathode comprised of Au@SiO₂ (core@shell) nanoparticles embedded within a Cu₂O nanowire network is constructed to exclusively examine the contribution from one such mechanism: electromagnetic near‐field enhancement. The influence of the local electromagnetic field intensity is correlated with the overall light‐harvesting efficiency of the device through variation of the SiO₂ shell thickness (5–22 nm) to systematically tailor the distance between the plasmonic Au nanoparticles and the Cu₂O nanowires. A threefold increase in device photocurrent is achieved upon integrating the Au@SiO₂ nanoparticles into the Cu₂O nanowire network, further enabling a 40% reduction in semiconductor film thickness while maintaining photocathode performance. Photoelectrochemical results are further correlated with photoluminescence studies and optical simulations to confirm that the near‐field enhancement is the sole mechanism responsible for increased light absorption in the plasmonic photocathode.     

Interface Engineering of Hierarchical Branched Mo‐Doped Ni3S2/NixPy Hollow Heterostructure Nanorods for Efficient Overall Water Splitting

Rational design and construction of bifunctional electrocatalysts with excellent activity and durability is imperative for water splitting. Herein, a novel top‐down strategy to realize a hierarchical branched Mo‐doped sulfide/phosphide heterostructure (Mo‐Ni₃S₂/Ni_xP_y hollow nanorods), by partially phosphating Mo‐Ni₃S₂/NF flower clusters, is proposed. Benefitting from the optimized electronic structure configuration, hierarchical branched hollow nanorod structure, and abundant heterogeneous interfaces, the as‐obtained multisite Mo‐Ni₃S₂/Ni_xP_y/NF electrode has remarkable stability and bifunctional electrocatalytic activity in the hydrogen evolution reaction (HER)/oxygen evolution reaction (OER) in 1 m KOH solutions. It possesses an extremely low overpotential of 238 mV at the current density of 50 mA cm^?2 for OER. Importantly, when assembled as anode and cathode simultaneously, it merely requires an ultralow cell voltage of 1.46 V to achieve the current density of 10 mA cm^?2, with excellent durability for over 72 h, outperforming most of the reported Ni‐based bifunctional materials. Density functional theory results further confirm that the doped heterostructure can synergistically optimize Gibbs free energies of H and O‐containing intermediates (OH*, O*, and OOH*) during HER and OER processes, thus accelerating the catalytic kinetics of electrochemical water splitting. This work demonstrates the importance of the rational combination of metal doping and interface engineering for advanced catalytic materials.     

Hydride‐Enhanced CO2 Methanation: Water‐Stable BaTiO2.4H0.6 as a New Support

Catalytic CO₂ hydrogenation to CH₄ provides a promising approach to producing natural gas, and reducing the emissions of global CO₂. However, the efficiency of catalytic CO₂ methanation is limited by slow kinetics at low temperatures. This study first demonstrates that an air‐ and water‐stable perovskite oxyhydride BaTiO_2.4H_0.6 could function as an active support material for Ni‐, Ru‐based catalysts for CO₂ methanation at 300–350 °C, a relatively lower temperature. With the oxyhydride support, the activity for Ni and Ru increases by a factor of 2–7 when compared to the BaTiO₃ oxide support. Kinetic analysis shows reduced H₂ poisoning probably due to spillover, implying that the activity change is due to the kinetics being influenced by hydride. Furthermore, the oxyhydride‐supported Ni catalyst is also durable with its catalytic performance preserved for at least 10 h under a humid environment at elevated temperatures. It is anticipated that these perovskite oxyhydrides will shed new light on the design of high‐efficiency metal‐based catalysts for water‐involved catalytic reactions.     

Electrochemical CO2 Reduction Using Electrons Generated from Photoelectrocatalytic Phenol Oxidation

Electrochemical CO₂ reduction (ECCO₂R) requires electrons, for example, from oxygen evolution reaction (OER). However, such a multiple‐electron‐involved reaction is complicated and kinetically slow, leading to high overpotential. Herein, OER is replaced with photoelectrocatalytic phenol oxidation reaction (PECPOR) that provides electrons for ECCO₂R. In an integrated cell, ECCO₂R is conducted on the cathode of Cu nanowires and PECPOR is performed on the anode of SnO₂ and Sb coated TiO₂ nanotubes. Significant improvement of ECCO₂R into CO and hydrocarbons is realized when PECPOR is conducted at a high current density. The use of this integrated system results in the reduction of the specific energy consumption by a factor of 51.33%, compared with the utilization of two half‐cells for individual ECCO₂R and PECPOR. This study thus proposes a novel strategy to couple ECCO₂R with PECPOR and eventually to tackle the problems of environmental pollution and energy crisis.     

Ni Strongly Coupled with Mo2C Encapsulated in Nitrogen‐Doped Carbon Nanofibers as Robust Bifunctional Catalyst for Overall Water Splitting

It is urgently required to develop highly efficient and stable bifunctional non‐noble metal electrocatalysts for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) for water splitting. In this study, a facile electrospinning followed by a post‐carbonization treatment to synthesize nitrogen‐doped carbon nanofibers (NCNFs) integrated with Ni and Mo₂C nanoparticles (Ni/Mo₂C‐NCNFs) as water splitting electrocatalysts is developed. Owing to the strong hydrogen binding energy on Mo₂C and high electrical conductivity of Ni, synergetic effect between Ni and Mo₂C nanoparticles significantly promote both HER and OER activities. The optimized hybrid (Ni/Mo₂C(1:2)‐NCNFs) delivers low overpotentials of 143 mV for HER and 288 mV for OER at a current density of 10 mA cm^?2. An alkaline electrolyzer with Ni/Mo₂C(1:2)‐NCNFs as catalysts for both anode and cathode exhibits a current density of 10 mA cm^?2 at a voltage of 1.64 V, which is only 0.07 V larger than the benchmark of Pt/C‐RuO₂ electrodes. In addition, an outstanding long‐term durability during 100 h testing without obvious degradation is achieved, which is superior to most of the noble‐metal‐free electrocatalysts reported to date. This work provides a simple and effective approach for the preparation of low‐cost and high‐performance bifunctional electrocatalysts for efficient overall water splitting.