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This review introduces fundamental aspects of the electrocatalytic CO2RR process together with a systematic examination of recent developments in Cu-based electrocatalysts for the electroreduction of CO2 to various high-value multicarbon products.

The high activity of the electrodeposited Ni/Ru hydroxide hybrid was attributed to the interaction between Ru and oxidized Ni species formed in the Ru–O–Ni matrix, which promoted the conversion of nitrate to ammonia through the synergistic effect.

Green hydrogen production and CO2 fixation have been identified as the fundamental techniques for sustainable economy. The open challenge is to develop high performance catalysts for hydrogen evolution reaction (HER) and CO2 electroreduction (CO2ER) to valuable chemicals. Under such context, this work reported computational efforts to design promising electrocatalyst for HER and CO2ER based on the swarm-intelligence algorithm. Among the family of transition-metal phosphides (TMPs), Pt2P3 monolayer has been identified as excellent bifunctional catalysts due to high stability, excellent conductivity and superior catalytic performance. Different from typical d-block catalysts, p-band center presented by P atoms within Pt2P3 monolayer plays the essential role for its reactivity towards HER and CO2ER, underlining the key value of p-electrons in advanced catalyst design and thus providing a promising strategy to further develop novel catalysts made of p-block elements for various energy applications.

Carbon dioxide reduction (CRR) is an attractive strategy for alleviating global warming and producing valuable fuels. In this work, we study the catalytic conversion of CO2 to C1-C3 products on boron nanosheet in the presence of compressive strain by using density functional theory. Thermodynamic and microkinetic models are applied to demonstrate the favorable products, critical steps, and hydrogenation mechanisms. As demonstrated, the strain can turn metallic two-dimensional boron nanosheet to semiconductor, not only making boron sheets possess photo(electro)catalytic activity, but also improving energy efficiency and selectivity performance against hydrogen evolution reaction. By introducing the aqueous electrolytes, the hydrated alkali cations not only effect on the CO2 concentration, but also produce a bigger surface charge density and stronger interfacial electric filed. Especially, the selectivity of C2+ products is enhanced with the increase of alkali cations size by decreasing the kinetic barrier for CO dimerization and stabilizing the intermediates. The results highlight the significance of metal-free catalysts for CRR by the photoelectrochemical method and provide novel avenues for the development of new solar-energy utilization catalysts.

Confined metal clusters as sub-nanometer reactors for electrocatalytic N2 reduction reaction (eNRR) have received increasing attention due to the unique metal-metal interaction and higher activity than single-atom catalysts. Herein, the inspiration of the superior capacitance and unique microenvironment with regular surface cavities of the porous boron nitride (p-BN) nanosheets, we systematically studied the catalytic activity for NRR of transition-metal single-clusters in the triplet form (V3, Fe3, Mo3 and W3) confined in the surface cavities of the p-BN sheets by spin-polarized density functional theory (DFT) calculations. After a two-step screening strategy, Mo3@p-BN was found to have high catalytic activity and selectivity with a rather low limiting potential (–0.34 V) for the NRR. The anchored Mo3 single-cluster can be stably embedded on the surface cavities of the substrate preventing the diffusion of the active Mo atoms. More importantly, the Mo atoms in the Mo3 single-cluster would act as “cache” to accelerate electron transfer between active metal centers and nitrogen-containing intermediates via the intimate Mo-Mo interactions. The cooperation of Mo atoms can also provide a large number of occupied and unoccupied d orbitals to make the "donation–backdonation" mechanism more effective. This work not only provides a quite promising electrocatalyst for NRR, but also brings new insights into the rational design of triple-atom NRR catalysts.

Two-dimensional carbon nitride (2D-C3N4) nanosheets are promising materials in photocatalytic water splitting, but still suffer from easy agglomeration and fast photogenerated electron–hole pairs recombination. To tackle this issue, herein, a hierarchical Nb2O5/2D-C3N4 heterostructure is precisely constructed and the built-in electric field between Nb2O5 and 2D-C3N4 can provide the driving force to separate/transfer the charge carriers efficiently. Moreover, the strongly Lewis acidic Nb2O5 can adsorb TEOA molecules on its surface at locally high concentrations to facilitate the oxidation reaction kinetics under irradiation, resulting in efficient photogenerated electrons-holes separation and exceptional photocatalytic hydrogen evolution. As expected, the champion Nb2O5/2D-C3N4 heterostructure achieves an exceptional H2 evolution rate of 31.6 mmol g–1 h−1, which is 213.6 times and 4.3 times higher than that of pristine Nb2O5 and 2D-C3N4, respectively. Moreover, the champion heterostructure possesses a high apparent quantum efficiency (AQE) of 45.08% at λ = 405 nm and superior cycling stability. Furthermore, a possible photocatalytic mechanism of the energy band alignment at the hetero-interface is proposed based on the systematical characterizations accompanied by density functional theory (DFT) calculations. This work paves the way for the precise construction of a high-quality heterostructured photocatalyst with efficient charge separation to boost hydrogen production.

Activating water and methanol is crucial in numerous catalytic, electrocatalytic, and photocatalytic reactions. Despite extensive research, the optimal active sites for water/methanol activation are yet to be unequivocally elucidated. Here, we combine transition-state searches and electronic charge analyses on various structurally different materials to identify two features of favorable O–H bond cleavage in H2O, CH3OH, and hydroxyl: (1) low barriers appear when the charge of H moieties remains approximately constant during the dissociation process, as observed on metal oxides, MXenes, and metal/oxide interfaces. Such favorable kinetics is closely related to adsorbate/substrate hydrogen bonding and is enhanced by nearly linear O–H–O angles and short O–H distances. (2) Fast dissociation is observed when the rotation of O–H bonds is facile, which is favored by weak adsorbate binding and effective orbital overlap. Interestingly, we find that the two features are energetically proportional. Finally, we find conspicuous differences between H2O/CH3OH and OH activation, which hints toward the use of carefully engineered interfaces.

Electrochemical reduction of nitrogen is considered a promising route for achieving green and sustainable ammonia synthesis under ambient conditions.

The mechanism of regulating the spin order of transition metal embedded-MXenes for boosting electrocatalytic nitrogen reduction to ammonia.

TiO2@g-C3N4 core/shell fibers with a continuous g-C3N4 layer packing around exhibit high photocatalytic efficiency toward H2 production and RhB degradation due to the intimate core/shell structure with a high-quality TiO2/g-C3N4 heterojunction.

High-resolution neutron radiography provides novel and stirring opportunities to investigate the structures of light elements encased by heavy elements. For this study, a series of Gd2O2S:Tb, F particles were prepared using a high-temperature solid phase method and then used as a scintillation screen. Upon reaching 293 nm excitation, a bright green emission originated from the Tb3+ luminescence center. The level of F doping affected the fluorescence intensity. When the F doping level was 8 mol%, the fluorescence intensity was at its highest. The absolute quantum yield of the synthesized particles reached as high as 77.21%. Gd2O2S:Tb, F particles were applied to the scintillation screen, showing a resolution on the neutron radiograph as high as 12 μm. These results suggest that the highly efficient Gd2O2S:Tb, F particles are promising scintillators for the purposes of cold neutron radiography.

Humic substances (HS) are the most abundant forms of natural organic matter on the earth surface. Comprised of decomposed plant and animal materials rich in carbon, oxygen, hydrogen, nitrogen, and sulfur complexes, HS facilitate global carbon and nitrogen cycling and the transport of anthropogenic contaminants. While it is known that HS also interact with organisms at different trophic levels to produce beneficial and harmful effects whether HS exert these biological effects through accumulation remains unknown. Current radiolabeling techniques, which only detect the amount of accumulated radiolabels, cannot visualize the transport and accumulation behavior of HS. Here, using a label-free method based on pump-probe microscopy, we show HS entered the protozoan

Molybdenum carbide (Mo

Electroreduction of CO2 to valuable multicarbon (C2+) products is a highly attractive way to utilize and divert emitted CO2. However, a major fraction of C2+ selectivity is confined to less than 90% by the difficulty of coupling C-C bonds efficiently. Herein, we identify the stable Cu0/Cu2+ interfaces derived from copper phosphates-based (CuPO) electrocatalysts, which can facilitate C2+ production with a low-energy pathway of OC-CHO coupling verified by in situ spectra studies and theoretical calculations. The CuPO precatalyst shows a high Faradaic efficiency (FE) of 69.7% towards C2H4 in an H-cell, and exhibits a significant FEC2+ of 90.9% under industrially relevant current density (j = -350 mA cm-2) in a flow cell configuration. The stable Cu0/Cu2+ interface breaks new ground for the structural design of electrocatalysts and the construction of synergistic active sites to improve the activity and selectivity of valuable C2+ products.

Catalyzed oxidative C-C bond coupling reactions play an important role in the chemical synthesis of complex natural products of medicinal importance. However, the poor functional group tolerance renders them unfit for the synthesis of naturally occurring polyphenolic flavones. We find that molecular oxygen in alkaline water acts as a hydrogen atom acceptor and oxidant in catalyst-free (without added catalyst) oxidative coupling of luteolin and other flavones. By this facile method, we achieve the synthesis of a small collection of flavone dimers and trimers including naturally occurring dicranolomin, philonotisflavone, dehydrohegoflavone, distichumtriluteolin, and cyclodistichumtriluteolin. Mechanistic studies using both experimental and computational chemistry uncover the underlying reasons for optimal pH, oxygen availability, and counter-cations that define the success of the reaction. We expect our reaction opens up a green and sustainable way to synthesize flavonoid dimers and oligomers using the readily available monomeric flavonoids isolated from biomass and exploiting their use for health care products and treatment of diseases.

Electrocatalytic nitrogen reduction reaction (eNRR) is a promising method for the sustainable production of ammonia as an alternative to the traditional energy-intensive Haber-Bosch process. In this work, an efficient strategy by atomic spin regulation to promote NRR through Fe-transition metal (TM) hybrid heteronuclear dual-atom catalysts has been studied. By means of DFT computations, the stability, activity, and selectivity of 30 kinds of Fe-based dual-atoms anchored on N-doped porous graphene are systematically investigated to evaluate their catalytic performance. Fe/MoNC is screened as an excellent NRR catalyst with the limiting potentials of 0.63 V, and also suppresses HER. In the Fe/MoNC, the neighboring Fe atom regulates the spin state of the Mo center in MoN

Ammonia synthesis by electrochemical nitrogen reduction technique is an attractive alternative to traditional Haber-Bosch process. Currently, development of an efficient and effective electrocatalyst is one of the remaining key challenges. In this work, density functional theory (DFT) computations were systematically employed on double transition metal atoms (Fe, Co, Ni, Cu and Mo) anchored Graphdiyne (GDY) for nitrogen reduction reaction (NRR). The Co-Ni heteronuclear complex and Mo-Mo homonuclear complex showed the highest NRR activity while demonstrating synergistic effect of double atomic catalytic sites towards the promising NRR activity.

Hydrogen storage is one of the key challenges for hydrogen economy. Among various storage candidates, magnesium hydride (MgH2) offers excellent storage capacity and cost performance, but its sluggi...

Mineral apatite compounds have attracted significant interest due to their chemical stability and adjustable hexagonal structure, which makes them suitable as new photovoltaic functional materials. The band gap of natural apatite is ~ 5.45 eV, and such a large value limits their applications in the field of catalysis and energy devices. In this research, we designed a method to narrow the band gap via the tetrahedral substitution effect in apatite-based compounds. The density functional theory (DFT) and experimental investigation of the electronic and optical properties revealed that the continuous incorporation of [MO4]4– tetrahedrons (M = Si, Ge, Sn, and Mn) into the crystal lattice can significantly reduce the band gap. In particular, this phenomenon was observed when the [MnO4]4– tetrahedron replaces the [PO4]4– tetrahedron because of the formation of a Mn 3d-derived conduction band minimum (CBM) and interacts with other elements, leading to band broadening and obvious reduction of the band gap. This approach allowed us to propose a novel scheme in the band gap engineering of apatite-based compounds toward an entire spectral range modification.

This paper gives a comprehensive review of the recent progress on electrochemical energy storage devices using graphene oxide (GO). GO, a single sheet of graphite oxide, is a functionalised graphene, carrying many oxygen-containing groups. This endows GO with various unique features for versatile applications in batteries, capacitors and fuel cells. Specific applications are considered principally including use in electrodes as the active materials to enhance the performance or as substrates to diversify the structures, in solid-state electrolytes and membranes to improve the ionic conductivity and mechanical properties, and in interlayers to protect the electrodes, membranes or current collectors. Furthermore, the challenges and future prospects are discussed in the paper for encouraging further research and development of GO applications.

Highly efficient, durable, and earth-abundant photocatalysts are of great interest toward practical photocatalytic conversion reactions, such as hydrogen generation and CO2 reduction. In this work,...

The electrochemical CO

Electrochemical reduction of nitrogen is considered a promising route for achieving green and sustainable ammonia synthesis under ambient conditions. A transition metal atom loaded on N-doped graphene is commonly used in the nitrogen reduction reaction (NRR), but the effect of the graphene's coordination environment on electron transfer has rarely been studied. Herein, the NRR performance of Fe

Safe and effective storage of hydrogen fuel is a step toward a hydrogen economy. As a model storage media, magnesium hydride (MgH2) experiences sluggish dehydrogenation dynamics, although its stora...

Two-dimensional (2D) metal–organic frameworks (MOFs) serve as emerging electrocatalysts due to their high conductivity, chemical tunability, and accessibility of active sites. We herein proposed a series of 2D MOFs with different metal atoms and organic linkers with the formula M3C12X12 (M = Cr, Mo, and W; X = NH, O, S, and Se) to design efficient nitrogen reduction reaction (NRR) electrocatalysts. Our theoretical calculations showed that metal atoms in M3C12X12 can efficiently capture and activate N2 molecules. Among these candidates, W3C12X12 (X = O, S, and Se) show the best NRR performance due to their high activity and selectivity as well as low limiting potential (−0.59 V, −0.14 V, and −0.01 V, respectively). Moreover, we proposed a d-band center descriptor strategy to screen out the high activity and selectivity of M3C12X12 for the NRR. Therefore, our work not only demonstrates a class of promising electrocatalysts for the NRR but also provides a strategy for further predicting the catalytic activity of 2D MOFs.

Photocatalytic nitrogen reduction reaction (NRR) is a promising, green route to chemically reducing N2 into NH3 under ambient conditions, correlating to the N2 fixation process of nitrogenase enzymes. To achieve high-yield NRR with sunlight as the driving force, high-performance photocatalysts are essential. One-dimensional silicon nanowires (1D SiNWs) are a great photoelectric candidate, but inactive for NRR due to their inability to capture N2. In this study, we proposed SiNWs doped by p-block elements (B, C, P) to tune the affinity to N2 and demonstrated that two-coordinated boron (B2C) offers an ultra-low overpotential (η) of 0.34 V to catalyze full NRR, which is even much lower than that of flat benchmark Ru(0001) catalysts (η = 0.92 V). Moreover, aspects including suppressed hydrogen evolution reaction (HER), high-spin ground state of the B2C site, and decreased band gap after B-doping ensure the high selectivity and photocatalytic activity. Finally, this work not only shows the potential use of metal-free p-block element-based catalysts, but also would facilitate the development of 1D nanomaterials towards efficient reduction of N2 into NH3.

Ammonia (NH3) is a crucial chemical as a fertilizer and energy carrier, which is mainly produced by the traditional Haber–Bosch process that consumes hydrogen and leads to the emission of carbon dioxide. The electrochemical nitrogen reduction reaction (ENRR) is considered as an alternative method with low energy consumption and mild condition. However, the NH3 yield and faradaic efficiency (FE) of the electrocatalyst are dominated by the competition between the hydrogen evolution reaction (HER) and NRR. In order to achieve both high catalytic activity and high selectivity, the poor-performance catalyst needs to be improved via modification engineering. For the catalysts of oxygenated compounds, introducing oxygen vacancies (OVs) into the structure can enhance the catalytic property of NRR via regulating the local electronegativity and coordination environment. In this review, recent advances in the detection, preparation and application of OVs for NRR are summarized. We focus on the generating strategies of OVs and their evaluation method, including vacuum annealing, high-temperature hydrogen reduction, wet chemical, plasma treatment, and ion-doping strategy. Finally, the opportunities and challenges towards the suitable design of OVs in oxides for NRR are highlighted.

Modulating the microenvironment of single-atom catalysts (SACs) has been identified as an effective strategy to improve their performance in electrocatalysis. Here, by means of comprehensive density functional theory (DFT) computations, we systematically explored the effects of the coordination environment on the catalytic activity of single Mo atoms towards the nitrogen reduction reaction (NRR) for ammonia synthesis. Through comparing a large series of coordination combinations, we found that the Mo-based SAC with a unique B, O-dual coordination (Mo-B3O) exhibits the best NRR performance with ultralow limiting potential (−0.34 V), which preferably proceeds along the enzymatic pathway, with the initial hydrogenation (*N2 → *N2H) as the potential-limiting step. Moreover, the Mo-B3O can suppress the competing H2 production, exhibit high thermodynamic stability, and hold great promise for experimental synthesis. Our findings not only further enrich the family of SACs by controlling the local coordination, but also offer cost-effective opportunities for advancing sustainable NH3 production.

Optimizing the electrochemical carbon dioxide reduction reaction (CRR) to fuels is one of the most significant challenges in materials science and chemistry. Recently, single metal atom catalysts based on 2D materials have shown promise to improve the electroreduction performance of pristine 2D materials in the CRR. The physical origins of such performance enhancements are still poorly understood. Herein, we report the potential of a single Cu atom doped phosphorene catalyst for CO2 electroreduction based on density functional theory (DFT) calculations. The doping sites (hollow, bridge, and on-top) of Cu on phosphorene are investigated first. Phosphorene with a Cu atom anchored on the hollow site is chosen for further study. The pathways for different CRR products, including HCOOH, CO, CH3OH, and CH4, are examined via constructing free energy diagrams and via comparing the limiting potentials. CH4 is the most likely product after analysis of the adsorption energies and free energy pathways. Cu-Doped phosphorene in general shows improved CRR performance with lower limiting potential values. Cu doping leads to a decrease in the band gap value (about 0.2 eV), which is likely to be the physical origin of the CRR performance enhancement. Our study provides a novel promising CRR candidate catalyst based on phosphorene.