It is common that different crystal facets in metal and metal oxide nanocrystals display different catalytic performances, whereas such phenomena have been rarely documented in metal–organic ...frameworks (MOFs). Herein, we demonstrate for the first time that a nickel metal–organic layer (MOL) exposing rich (100) crystal facets (Ni‐MOL‐100) shows a much higher photocatalytic CO2‐to‐CO activity than the one exposing rich (010) crystal facets (Ni‐MOL‐010) and its bulky counterpart (bulky Ni‐MOF), with a catalytic activity up to 2.5 and 4.6 times more active than Ni‐MOL‐010 and bulky Ni‐MOF, respectively. Theoretical studies reveal that the two coordinatively unsaturated NiII ions with a close distance of 3.50 Å on the surface of Ni‐MOL‐100 enables synergistic catalysis, leading to more favorable energetics in CO2 reduction than that of Ni‐MOL‐010.
Crystal‐facet‐dependent catalytic performance for CO2 reduction has been observed in Ni‐based 2D MOLs. Ni‐MOL‐100 displays much higher catalytic activity than Ni‐MOL‐010, benefiting from the synergistic catalysis between two adjacent Ni sites in Ni‐MOL‐100.
Dual‐atom catalysts (DACs) have emerged as efficient electrocatalysts for CO2 reduction owing to the synergistic effect between the binary metal sites. However, rationally modulating the electronic ...structure of DACs to optimize the catalytic performance remains a great challenge. Herein, we report the electronic structure modulation of three Ni2 DACs (namely, Ni2−N7, Ni2−N5C2 and Ni2−N3C4) by the regulation of the coordination environments around the dual‐atom Ni2 centres. As a result, Ni2−N3C4 exhibits significantly improved electrocatalytic activity for CO2 reduction, not only better than the corresponding single‐atom Ni catalyst (Ni−N2C2), but also higher than Ni2−N7 and Ni2−N5C2 DACs. Density functional theory (DFT) calculations revealed that the high electrocatalytic activity of Ni2−N3C4 for CO2 reduction could be attributed to the electronic structure modulation to the Ni centre and the resulted proper binding energies to COOH* and CO* intermediates.
Three Ni2 dual‐atom catalysts (DACs) with electronic structures tailored by the regulation of the coordination environment of Ni atoms, have been prepared for electrocatalytic CO2 reduction. The optimal Ni2−N3C4 exhibits the highest performance for the reduction of CO2 to CO, highlighting the significance of the electronic structure for electrocatalytic CO2 reduction in DACs.
The solar‐driven CO2 reduction is a challenge in the field of “artificial photosynthesis”, as most catalysts display low activity and selectivity for CO2 reduction in water‐containing reaction ...systems as a result of competitive proton reduction. Herein, we report a dinuclear heterometallic complex, CoZn(OH)L1(ClO4)3 (CoZn), which shows extremely high photocatalytic activity and selectivity for CO2 reduction in water/acetonitrile solution. It achieves a selectivity of 98 % for CO2‐to‐CO conversion, with TON and TOF values of 65000 and 1.8 s−1, respectively, 4, 19, and 45‐fold higher than the values of corresponding dinuclear homometallic CoCo(OH)L1(ClO4)3 (CoCo), ZnZn(OH)L1(ClO4)3 (ZnZn), and mononuclear CoL2(CH3CN)(ClO4)2 (Co), respectively, under the same conditions. The increased photocatalytic performance of CoZn is due to the enhanced dinuclear metal synergistic catalysis (DMSC) effect between ZnII and CoII, which dramatically lowers the activation barriers of both transition states of CO2 reduction.
In sync with zinc: A dinuclear heterometallic CoZn catalyst shows much higher photocatalytic activity than the corresponding dinuclear homometallic CoCo and ZnZn catalysts, or the mononuclear Co and Zn catalysts for CO2 reduction under the same conditions. The high performance of the CoZn catalyst is due to the enhanced dinuclear metal synergistic catalysis (DMSC) effect between ZnII and CoII.
An extremely stable hydrogen-bonded organic framework, HOF-8, was fabricated. HOF-8 is not only thermally stable but also stable in water and common organic solvents. More interestingly, desolvated ...HOF-8 exhibits high CO2 adsorption as well as highly selective CO2 and C6H6 adsorption at ambient temperature.
A dinuclear cobalt complex Co2(OH)L1(ClO4)3 (1, L1=N(CH2)2NHCH2(m‐C6H4)CH2NH(CH2)23N) displays high selectivity and efficiency for the photocatalytic reduction of CO2 to CO in CH3CN/H2O (v/v=4:1) ...under a 450 nm LED light irradiation, with a light intensity of 100 mW cm−2. The selectivity reaches as high as 98 %, and the turnover numbers (TON) and turnover frequencies (TOF) reach as high as 16896 and 0.47 s−1, respectively, with the calculated quantum yield of 0.04 %. Such high activity can be attributed to the synergistic catalysis effect between two CoII ions within 1, which is strongly supported by the results of control experiments and DFT calculations.
CoCo catalysts: A dinuclear cobalt cryptate displays high selectivity and efficiency for the photocatalytic reduction of CO2 to CO in CH3CN/H2O solution under a 450 nm LED light irradiation, at a light intensity of 100 mW cm−2. The high catalytic efficiency originates from the synergistic catalysis effect between two CoII ions within the catalyst.
•Core scientific challenges in electrocatalytic water splitting were discussed.•Prussian blue analogues (PBAs) as electrocatalysts for water splitting.•PBA derived nanomaterials as electrocatalysts ...for water splitting.•Perspectives for PBA-based water-splitting electrocatalysts were put forward.
The electrocatalytic water splitting is considered as a prospect meaning to address the urgent energy and environmental problems. However, the electrocatalytic water splitting is greatly limited by the high overpotentials of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Especially, OER involves a complex multistep proton-coupled electron transfer process, which demands a high overpotential to accelerate this sluggish oxygen evolution kinetics. The high overpotentials for OER significantly decrease the efficiency of the overall water splitting. The OER half reaction has thus become the bottleneck of electrocatalytic overall water splitting. It is vital to synthesize highly active electrocatalysts to reduce the activation energy of the reaction and accelerate the generation of H2 and O2, thereby improving the efficiency of the overall water splitting. Prussian blue analogues (PBAs) are representative cyanide-based coordination polymer materials. PBAs possess open framework structures, large specific surface areas, adjustable metal active sites and uniform catalytic centers, showing promising application in electrocatalytic water splitting. Besides, benefiting from the unique structural features of PBAs, their derived electrocatalysts also have large specific surface areas and uniform active sites. Moreover, PBAs can serve as carbon and nitrogen sources. The doped N can regulate the electronic structure of surface active sites, enhancing the intrinsic activity of electrocatalysts. Therefore, the PBA-derived electrocatalysts also exhibit good catalytic performance for water splitting. In this review, we not only summarize the most recent advances on PBAs and their derivatives as electrocatalysts for water splitting, but also conclude the core scientific challenges faced in water splitting. Finally, we provide perspectives for the future research in this field, including catalyst design, catalytic system establishment and so on.
The mismatched fast‐electron‐slow‐proton process in the electrocatalytic oxygen evolution reaction (OER) severely restricts the catalytic efficiency. To overcome these issues, accelerating the proton ...transfer and elucidating the kinetic mechanism are highly sought after. Herein, inspired by photosystem II, we develop a family of OER electrocatalysts with FeO6/NiO6 units and carboxylate anions (TA2−) in the first and second coordination sphere, respectively. Benefiting from the synergistic effect of the metal units and TA2−, the optimized catalyst delivers superior activity with a low overpotential of 270 mV at 200 mA cm−2 and excellent cycling stability over 300 h. A proton‐transfer‐promotion mechanism is proposed by in situ Raman, catalytic tests, and theoretical calculations. The TA2− (proton acceptor) can mediate proton transfer pathways by preferentially accepting protons, which optimizes the O−H adsorption/activation process and reduces the kinetic barrier for O−O bond formation.
We developed an electrocatalytic model that is designed to obtain superior oxygen evolution reaction activity (270 mV at 200 mA cm−2) and cycle stability (over 300 h) by tuning the proton transfer pathway. The electron‐rich terephthalic acid anion located in the second coordination sphere of the active center can mediate proton transfer pathways by preferentially accepting protons, which reduces the kinetic barrier for O−O bond formation.
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•Dinuclear non-noble catalysts for water oxidation and CO2 reduction are reviewed.•The synergistic effects in dinuclear non-noble catalysts are emphasized.•Present limitations and ...possible perspective for the further progress are discussed.
The realization of artificial photosynthesis is of intense interest as it can be an effective solution to relieve the energy crisis. Besides hydrogen evolution and some organic oxidation reactions, water oxidation and CO2 reduction reactions are two crucial alternative half-reactions that can be coupled to form a classic artificial photosynthetic system. Both of them are energy-demanding and thus show slow reaction rates without appropriate catalysts. Dinuclear non-noble metal complexes are promising candidates as bio-inspired mediators to facilitate both reactions through the potential synergistic catalytic effect between two metal sites. In this Review, key advancements in dinuclear non-noble metal complexes as the molecular catalysts for water oxidation and CO2 reduction reactions have been highlighted to provide a future perspective.
The reduction of carbon dioxide (CO2) has been considered as an approach to mitigate global warming and to provide renewable carbon‐based fuels. Rational design of efficient, selective, and ...inexpensive catalysts with low overpotentials is urgently desired. In this study, four cobalt(II) tripodal complexes are tested as catalysts for CO2 reduction to CO in a MeCN/H2O (4:1 v/v) solution. The replacement of pyridyl groups in the ligands with less basic quinolinyl groups greatly reduces the required overpotential for CO2‐to‐CO conversion down to 200–380 mV. Benefitting from the low overpotentials, a photocatalyst system for CO2‐to‐CO conversion is successfully constructed, with an maximum turnover number (TON) of 10 650±750, a turnover frequency (TOF) of 1150±80 h−1, and almost 100 % selectivity to CO. These outstanding catalytic performances are further elucidated by DFT calculations.
Electric/light orchestration: Four cobalt complexes with tripodal ligands are utilized as high‐performance molecular electro‐ and photocatalysts for the reduction of CO2 to CO in a water‐containing system. By the introduction of less basic aromatic nitrogen donors in the tripodal ligands, the overpotentials can be reduced down to record low values of 200–380 mV, leading to high efficiency and selectivity for photocatalytic reduction of CO2 to CO.
2D lamellar materials can offer high surface area and abundant reactive sites, thus showing an appealing prospect in photocatalytic hydrogen evolution. However, it is still difficult to build ...cost‐efficient photocatalytic hydrogen evolution systems based on 2D materials. Herein, an in situ growth method is employed to build 2D/2D heterojunctions, with which 2D Ni‐based metal–organic layers (Ni‐MOLs) are closely grown on 2D porous CdS (P‐CdS) nanosheets, affording traditional P‐CdS/Ni‐MOL heterojunction materials. Impressively, the optimized P‐CdS/Ni‐MOL catalyst exhibits superior photocatalytic hydrogen evolution performance, with an H2 yield of 29.81 mmol g−1 h−1. This value is 7 and 2981 times higher than that of P‐CdS and Ni‐MOLs, respectively, and comparable to those of reported state of the art catalysts. Photocatalytic mechanism studies reveal that the enhanced photocatalytic performance can be attributed to the 2D/2D intimate interface between P‐CdS and Ni‐MOLs, which facilitates the fast charge carriers’ separation and transfer. This work provides a strategy to develop 2D MOL‐based photocatalysts for sustainable energy conversion.
The ultrathin structure and large specific surface area of the P‐CdS/Ni‐MOL composites are of great benefit for exposing more active sites and expanding contact surface area. In such a way, the recombination of photoinduced electrons/holes pairs can be efficiently inhibited. The synergistic effect of the intimate contact between P‐CdS and Ni‐MOLs can significantly enhance the photocatalytic H2 evolution performances.
