Molecular Photoelectrochemical Energy Storage Materials for Coupled Solar Batteries.

ConspectusSolar-to-electrochemical energy storage is one of the essential solar energy utilization pathways alongside solar-to-electricity and solar-to-chemical conversion. A coupled solar battery enables direct solar-to-electrochemical energy storage via photocoupled ion transfer using photoelectrochemical materials with light absorption/charge transfer and redox capabilities. Common photoelectrochemical materials face challenges due to insufficient solar spectrum utilization, which restricts their redox potential window and constrains energy conversion efficiency. In contrast, molecular photoelectrochemical energy storage materials are promising for their mechanism of exciton-involved redox reaction that allows for extra energy utilization from hot excitons generated by superbandgap excitation and localized heat after absorption of sub-bandgap photons. This enables more efficient redox reactions with a less restricted redox potentials window and, thus, better utilization of the full solar spectrum. Despite these advantages, practical application remains elusive due to the mismatch between the short lifetime of the charge separation state (µs). This mismatch results in a significant portion of the photogenerated charges recombining before participating in desired electrochemical energy storage reactions, leading to diminished overall efficiency. It is therefore highly important to develop molecular materials with intrinsic prolonged charge separation state and extrinsic effective mass-electron transfer to enable efficient coupled solar batteries for practical applications.In this Account, we begin with an introduction of the general solar-to-electrochemical energy storage concept based on molecular photoelectrochemical energy storage materials, highlighting the advantages of periodic oxidative donor-reductive acceptor porous aggregate structures that have synergistic implications on charge separation state lifetime extension and mass-electron transfer. We then present our earliest trial on the design and application of molecular photoelectrochemical energy storage materials, which stimulated our subsequent studies on tuning electron donor and acceptor structures for enhanced charge separation and diverse photoelectrochemical redox reactions. Moreover, we introduce the best practices in the design and assembly of various coupled solar battery devices, along with our literature contributions and progresses in solar-to-electrochemical energy storage efficiency (ηSES) over nearly the past decade. Finally, we conclude by highlighting the universality of our strategies as essential design principles, spanning from regulating long-lived charge separation states and photocoupled ion transfer processes in molecular materials to the construction of efficient coupled solar batteries. We offer perspectives on the synergy between photovoltage and redox potentials and the practical significance of 3D printing, providing key evaluation indicators for large-scale application. This Account provides molecular level insights for the construction of high-efficiency photoelectrochemical energy storage materials and guidance for practical solar-to-electrochemical energy storage applications.

Efficient Photocatalytic CO2 Reduction in Ellagic Acid-Based Covalent Organic Frameworks.

Employing covalent organic frameworks (COFs) for the photocatalytic CO2 reduction reaction (CDRR) to generate high-value chemical fuels and mitigate greenhouse gas emissions represents a sustainable catalytic conversion approach. However, achieving superior photocatalytic CDRR performance is hindered by the challenges of low charge separation efficiency, poor stability, and high preparation costs associated with COFs. Herein, in this work, we utilized perfluorinated metallophthalocyanine (MPcF16) and the organic biomolecule compound ellagic acid (EA) as building blocks to actualize functional covalent organic frameworks (COFs) named EPM-COF (M = Co, Ni, Cu). The designed EPCo-COF, featuring cobalt metal active sites, demonstrated an impressive CO production rate and selectivity in the photocatalytic CO2 reduction reaction (CDRR). Moreover, following alkaline treatment (EPCo-COF-AT), the COF exposed carboxylic acid anion (COO-) and hydroxyl group (OH), thereby enhancing the electron-donating capability of EA. This modification achieved a heightened CO production rate of 17.7 mmol g-1 h-1 with an outstanding CO selectivity of 97.8% in efficient photocatalytic CDRR. Theoretical calculations further illustrated that EPCo-COF-AT functionalized with COO- and OH can effectively alleviate the energy barriers involved in the CDRR process, which facilitates the proton-coupled electron transfer processes and enhances the photocatalytic performance on the cobalt active sites within EPCo-COF-AT.

Temporally Decoupled Ammonia Splitting by a Zn-NH3 Battery with an Ammonia Oxidation/Hydrogen Evolution Bifunctional Electrocatalyst as a Cathode.

Ammonia splitting to hydrogen is a decisive route for hydrogen economy but is seriously limited by the complex device and low efficiency. Here, we design and propose a new rechargeable Zn-NH3 battery based on temporally decoupled ammonia splitting to achieve efficient NH3-to-H2 conversion. In this system, ammonia is oxidized into nitrogen during cathodic charging (2NH3 + 6OH- → N2 + 6H2O + 6e-) with external electrical energy conversion and storage, while during cathodic discharging, water is reduced to hydrogen (2H2O + 2e- → H2 + 2OH-) with electrical energy generation. In this loop, continuous and efficient H2 production without separation and purification is achieved. With the help of the ammonia oxidation reaction (AOR) and hydrogen evolution reaction (HER) bifunctional catalyst of Mo2C/NiCu@C, a rechargeable Zn-NH3 battery is realized that exhibits a high NH3-to-H2 FE of 91.6% with outstanding durability for 900 cycles (300 h) at 20 mA/cm2, enabling efficient and continuous NH3-to-H2 conversion.

Development, Essence, and Application of a Metal-Catalysis Battery.

ConspectusIn the pursuit of maximizing the energy supply and sustainable energy development, high-energy-density energy storage systems beyond lithium-ion batteries are surging. The metal-catalysis battery, composed of a metal anode, electrolyte, and redox-coupled electrocatalyst cathode with gas, liquid, or solid as active reactants, is regarded as a promising energy storage and conversion system due to its dual functions of energy storage and chemical production. In this system, with the assistance of a redox-coupled catalyst, during discharging, the reduction potential energy of the metal anode is converted into chemicals along with electrical energy generation, while the external electrical energy is translated to the reduction potential energy of the metal anode and the oxidation potential energy of the reactants during charging. In this loop, the electrical energy and sometimes chemicals can be generated simultaneously. Although intensive effort has been devoted to the exploration of redox-coupled catalysts, the essence of the metal-catalysis battery, which is the prerequisite for further development and application, has been overlooked.In this Account, we present the journey of the metal-catalysis battery from development to essence and application and propose that the metal-catalysis battery system, which combines energy storage and electrocatalytic redox reactions with the characteristics of temporal decoupling and spatial coupling and an energy-conversion paradigm from electrical energy to chemicals via electrochemical energy storage, is achieved. First, inspired by the Zn-air/Li-air battery, we developed and realized Li-CO2/Zn-CO2 batteries and enriched the functions of the metal-catalysis battery from energy storage to chemical production. Based on OER/ORR and OER/CDRR catalysts, we have further explored OER/NO3-RR and HzOR/HER coupled catalysts and developed Zn-nitrate and Zn-hydrazine batteries. By extending the redox-coupled electrocatalyst systems from O, C species to N species and others, the metal-catalysis battery systems would develop from metal-Ox, Cx to metal-Nx and other batteries. Then, from Zn-CO2 and Zn-hydrazine batteries, we found that the overall reaction is decoupled into two separate reduction and oxidation reactions via the cathodic discharge and charge processes, and we further extracted the essence of the metal-catalysis battery, namely, the temporal-decouple and spatial-couple (TD-SC) mechanism, which is completely opposite to the conventional temporal couple and spatial decouple in electrochemical water splitting. Based on the TD-SC mechanism, we developed various applications of metal-catalysis batteries for the green and efficient synthesis of fine chemicals by modifying the metal anode and redox-coupled catalysts and electrolytes, including the Li-N2/H2 battery for NH3 synthesis and the organic Li-N2 battery for fine chemical synthesis. Finally, the main challenges and the possible opportunities for the metal-catalysis battery are discussed, including the rational design of highly efficient redox-coupled electrocatalysts and green electrochemical synthesis. The deep insight into the metal-catalysis battery will provide an alternative approach to energy storage and chemical production.

Cyanide-based Covalent Organic Frameworks for Enhanced Overall Photocatalytic Hydrogen Peroxide Production.

Photocatalytic oxygen reduction to produce hydrogen peroxide (H2O2) is a promising route to providing oxidants for various industrial applications. However, the lack of well-designed photocatalysts for efficient overall H2O2 production in pure water has impeded ongoing research and practical thrusts. Here we present a cyanide-based covalent organic framework (TBTN-COFs) combining 2,4,6-trimethylbenzene-1,3,5-tricarbonitrile (TBTN) and benzotrithiophene-2,5,8-tricarbaldehyde (BTT) building blocks with water-affinity and charge-separation. The ultrafast intramolecular electron transfer (<500 fs) and prolonged excited state lifetime (748 ps) can be realized by TBTN-COF, resulting in a hole accumulated BTT and electron-rich TBTN building block. Under one sun, the 11013 µmol h-1 g-1 yield rate of H2O2 can be achieved without any sacrificial agent, outperforming most previous reports. Furthermore, the DFT calculation and in situ DRIFTS spectrums suggesting a Yeager-type absorption of *O2⋅- intermediate in the cyanide active site, which prohibits the formation of superoxide radical and revealing a favored H2O2 production pathway.

Molecular Engineering of Methylated Sulfone-based Covalent Organic Frameworks for Back-reaction Inhibited Photocatalytic Overall Water Splitting.

Solar-to-hydrogen (H2) and oxygen (O2) conversion via photocatalytic overall water splitting (OWS) holds great promise for a sustainable fuel economy, but has been challenged by the backward O2 reduction reaction (ORR) due to its favored proton-coupled electron transfer (PCET) dynamics. Here, we report that molecular engineering by methylation inhibits the backward ORR of molecular photocatalysts and enables efficient OWS process. As demonstrated by a benchmark sulfone-based covalent organic framework (COF) photocatalyst, the precise methylation of its O2 adsorption sites effectively blocks electron transfer and increases the barrier for hydrogen intermediate desorption that cooperatively obstructs the PCET process of ORR. Methylation also repels electrons to the neighboring photocatalytic sulfone group that promotes the forward H2 evolution. The resultant DS-COF achieves an impressive inhibition of about 70% of the backward reaction and a three-fold enhancement of the OWS performance with a H2 evolution rate of 124.7 µmol h-1 g-1, ranking among the highest reported for organic photocatalysts. This work provides insights for engineering photocatalysts at the molecular level for efficient solar-to-fuel conversion.

Coupling Electron Transfer and Redox Site in Boranil Covalent Organic Framework Toward Boosting Photocatalytic Water Oxidation.

The efficient polymeric semiconducting photocatalyst for solar-driven sluggish kinetics with multielectron transfer oxygen evolution has spurred scientific interest. However, existing photocatalysts limited by π-conjugations, visible-light harvest, and charge transfer often compromise the O2 production rate. Herein, we introduced an alternative strategy involving a boranil functionalized-based fully π-conjugated ordered donor and acceptor (D-A) covalent organic frameworks (Ni-TAPP-COF-BF2 ) photocatalyst. The co-catalyst-free Ni-TAPP-COF-BF2 exhibits an excellent ~11-fold photocatalytic water oxidation rate, reaching 1404 µmol g-1 h-1 under visible light irradiation compared to pristine Ni-TAPP-COF (123 µmol g-1 h-1 ) alone and surpasses to reported organic frameworks counterpart. Both experimental and theoretical results demonstrate that the push/pull mechanism (metalloporphyrin/BF2 ) is responsible for the appropriate light-harvesting properties and extending π-conjugation through chelating BF2 moieties. This strategy benefits in narrowing band structure, improving photo-induced charge separation, and prolonged charge recombination. Further, the lower spin magnetic moment of M-TAPP-COF-BF2 and the closer d-band center of metal sites toward the Fermi level lead to a lower energy barrier for *O intermediate. Reveal the potential of the functionalization strategy and opens up an alternative approach for engineering future photocatalysts in energy conversion applications.

Decoupled Artificial Photosynthesis via a Catalysis-Redox Coupled COF||BiVO4 Photoelectrochemical Device.

Artificial photosynthesis is an attractive approach to direct fuel production from sunlight. However, the simultaneous O2 evolution reaction (OER) and CO2 reduction reaction (CDRR) present challenges for product separation and safety. Herein, we propose a strategy to temporally decouple artificial photosynthesis through photoelectrochemical energy storage. We utilized a covalent organic framework (DTCo-COF) with redox-active electron donors (-C-OH moieties) and catalytically active electron acceptors (cobalt-porphyrin) to enable reversible -C-OH/-C═O redox reaction and redox-promoted CO2-to-CO photoreduction. Integrating the COF photocathode with an OER photoanode in a photoelectrochemical device allows the effective storage of OER-generated electrons and protons by -C═O groups. These stored charges can be later employed for CDRR while regenerating -C═O to complete the loop, thus enabling on-demand and separate production of O2 or solar fuels. Our work sets the stage for advancements in decoupled artificial photosynthesis and the development of more efficient solar fuel production technologies.

Photoelectrochemical energy storage materials: design principles and functional devices towards direct solar to electrochemical energy storage.

Advanced solar energy utilization technologies have been booming for carbon-neutral and renewable society development. Photovoltaic cells now hold the highest potential for widespread sustainable electricity production and photo(electro)catalytic cells could supply various chemicals. However, both of them require the connection of energy storage devices or matter to compensate for intermittent sunlight, suffering from complicated structures and external energy loss. Newly developed photoelectrochemical energy storage (PES) devices can effectively convert and store solar energy in one two-electrode battery, simplifying the configuration and decreasing the external energy loss. Based on PES materials, the PES devices could realize direct solar-to-electrochemical energy storage, which is fundamentally different from photo(electro)catalytic cells (solar-to-chemical energy conversion) and photovoltaic cells (solar-to-electricity energy conversion). This review summarizes a critically selected overview of advanced PES materials, the key to direct solar to electrochemical energy storage technology, with the focus on the research progress in PES processes and design principles. Based on the specific discussions of the performance metrics, the bottlenecks of PES devices, including low efficiency and deteriorative stability, are also discussed. Finally, several perspectives of potential strategies to overcome the bottlenecks and realize practical photoelectrochemical energy storage devices are presented.

A Pre-Grasping Motion Planning Method Based on Improved Artificial Potential Field for Continuum Robots.

Secure and reliable active debris removal methods are crucial for maintaining the stability of the space environment. Continuum robots, with their hyper-redundant degrees of freedom, offer the ability to capture targets of varying sizes and shapes through whole-arm grasping, making them well-suited for active debris removal missions. This paper proposes a pre-grasping motion planning method for continuum robots based on an improved artificial potential field to restrict the movement area of the grasping target and prevent its escape during the pre-grasping phase. The analysis of the grasping workspace ensures that the target is within the workspace when starting the pre-grasping motion planning by dividing the continuum robot into delivery and grasping segments. An improved artificial potential field is proposed to guide the continuum robot in surrounding the target and creating a grasping area. Specifically, the improved artificial potential field consists of a spatial rotating potential field, an attractive potential field incorporating position and posture potential fields, and a repulsive potential field. The simulation results demonstrate the effectiveness of the proposed method. A comparison of motion planning results between methods that disregard and consider the posture potential field shows that the inclusion of the posture potential field improves the performance of pre-grasping motion planning for spatial targets, achieving a success rate of up to 97.8%.

Decoupled Artificial Photosynthesis.

Natural photosynthesis (NP) generates oxygen and carbohydrates from water and CO2 utilizing solar energy to nourish lives and balance CO2 levels. Following nature, artificial photosynthesis (AP), typically, overall water or CO2 splitting, produces fuels and chemicals from renewable energy. However, hydrogen evolution or CO2 reduction is inherently coupled with kinetically sluggish water oxidation, lowering efficiencies and raising safety concerns. Decoupled systems have thus emerged. In this review, we elaborate how decoupled artificial photosynthesis (DAP) evolves from NP and AP and unveil their distinct photoelectrochemical mechanisms in energy capture, transduction and conversion. Advances of AP and DAP are summarized in terms of photochemical (PC), photoelectrochemical (PEC), and photovoltaic-electrochemical (PV-EC) catalysis based on material and device design. The energy transduction process of DAP is emphasized. Challenges and perspectives on future researches are also presented.

Coupled Solar Battery with 6.9 % Efficiency.

Solar-to-electrochemical energy storage in solar batteries is an important solar utilization technology comparable to solar-to-electricity (solar cells) and solar-to-fuel (photocatalytic cells) conversion. Unlike the indirect approach of integrated solar flow batteries combining photoelectrodes with redox-electrodes, coupled solar batteries enable direct solar energy storage, but are hampered by low efficiency due to rapid charge recombination of materials and misaligned energy levels between electrodes. Herein, we propose a design for a coupled solar battery that intercouples two photo-coupled ion transfer (PCIT) reactions through electron-ion transfer upon co-photo-pumping of photoelectrochemical storage cathode and anode. We used a representative covalent organic framework (COF) to achieve efficient charge separation and directional charge transfer between two band-matched photoelectrochemical storage electrodes, with a photovoltage sufficient for COF dual-redox reactions. By pumping these electrodes, the coupled solar battery stores solar energy via two synergistic PCIT reactions of electron-proton-relayed COF oxidation and reduction, and the stored solar energy is released as electrochemical energy during COF regeneration in discharge while interlocking the loops. A breakthrough in efficiency (6.9 %) was achieved, adaptive to a large-area (56 cm2 ) tandem device. The presented photo-intercoupled electron-ion transfer (PIEIT) mechanism provides expandable paths toward practical solar-to-electrochemical energy storage.

Overcoming the Trade-Off between C2 H2 Sorption and Separation Performance by Regulating Metal-Alkyne Chemical Interaction in Metal-Organic Frameworks.

Designing porous materials for C2 H2 purification and safe storage is essential research for industrial utilization. We emphatically regulate the metal-alkyne interaction of PdII and PtII on C2 H2 sorption and C2 H2 /CO2 separation in two isostructural NbO metal-organic frameworks (MOFs), Pd/Cu-PDA and Pt/Cu-PDA. The experimental investigations and systematic theoretical calculations reveal that PdII in Pd/Cu-PDA undergoes spontaneous chemical reaction with C2 H2 , leading to irreversible structural collapse and loss of C2 H2 /CO2 sorption and separation. Contrarily, PtII in Pt/Cu-PDA shows strong di-σ bond interaction with C2 H2 to form specific π-complexation, contributing to high C2 H2 capture (28.7 cm3 g-1 at 0.01 bar and 153 cm3 g-1 at 1 bar). The reusable Pt/Cu-PDA efficiently separates C2 H2 from C2 H2 /CO2 mixtures with satisfying selectivity and C2 H2 capacity (37 min g-1 ). This research provides valuable insight into designing high-performance MOFs for gas sorption and separation.

A Photoresponsive Battery Based on a Redox-Coupled Covalent-Organic-Framework Hybrid Photoelectrochemical Cathode.

Photoresponsive batteries promise flexible and low-cost solar-to-electrochemical energy storage (SES), but suffer from a limited SES efficiency due to rapid charge recombination and sluggish redox. Here, we present a porous-shell/core hybrid of covalent organic framework@carbon nanotube. This hybrid ensures long-lived separated charges (τave =3.0 ns) by an electron transfer relay starting from the donor-acceptor molecules to the nanoscale heterojunction. These charges are further allowed to drive high-rate redox of -C=O/-C-O- and -C-N/-C=N+ with facile kinetics. Equipped with this photoelectrochemical cathode, a photoresponsive aqueous battery shows a 5-fold enhancement in SES efficiency (1.1 % at 1 sun) over their counterparts. It is unveiled that the electron relay favors the formation of electron-enriching -C-O- and hole-enriching -C=N+ groups responsible for photoelectrochemical Zn2+ and OTf- storage cascade; and further, the general photo coupled ions transfer (PCIT) process is proposed. This work presents an inspiring photoelectrochemical cathode design and theoretical insight for photoresponsive batteries.

Recent Development of CO2 Electrochemistry from Li-CO2 Batteries to Zn-CO2 Batteries.

Metal-CO2 batteries with CO2 as cathode active species give rise to opportunities to deal with energy and environmental issues simultaneously. This technology is more appealing when CO2 is flexibly reduced to chemicals and fuels driven by surplus electricity because it represents a low-cost and controllable approach to maximized electricity utilization and value-added CO2 utilization. Nonaqueous metal-CO2 batteries exhibited high discharge voltage and capacity with carbon and oxalate as reduction products from CO2 electrochemistry that lacks proton. In contrast, aqueous Zn-CO2 batteries implemented flexible CO2 electrochemistry for more value-added products accompanied by energy storage based on a proton-coupled electron transfer mechanism. In this Account, we have exemplified our recent results in the development of CO2 electrochemistry from nonaqueous Li-CO2 batteries to aqueous Zn-CO2 batteries toward practical value-added CO2 conversion. Aimed at the challengingly limited CO2 electrochemistry and high cost of nonaqueous Li-CO2 batteries, we proposed aqueous Zn-CO2 batteries. Our previous works on nonaqueous Li-CO2 batteries, aqueous Zn-air batteries, and aqueous CO2 reduction electrocatalysts further shed light on battery mechanism, device construction, and electrocatalyst design. For example, bipolar membranes maintain the stability of the basic anolyte and neutral catholyte, as well as the kinetics of ion transport at the same time, forming the device base for aqueous Zn-CO2 batteries. Moreover, in terms of the electrocatalyst catalyzing both discharge and charge reactions on the cathode, the design of multifunctional electrocatalysts is of great importance for not only CO2 electrochemistry but also spontaneous discharge and energy efficiency of aqueous Zn-CO2 batteries. We have explored a series of multifunctional electrocatalyst cathodes, including noble metal, transition metal, and metal-free materials, all of which facilitated CO2 electrochemistry in aqueous Zn-CO2 batteries with value-added carbon-based products. Meanwhile, several operating models for practical complicated situations are presented, such as rechargeable, reversible, dual-model, and solid-state batteries. Zn-CO2 batteries with different models require different design mechanisms for electrocatalyst cathodes. Reversible aqueous Zn-CO2 batteries with HCOOH generation were enabled by electrocatalysts capable of catalyzing the interconversion of CO2 and HCOOH at low overpotentials, rechargeable aqueous Zn-CO2 batteries were allowed by electrocatalysts capable of catalyzing efficient CO2 reduction and O2 evolution, and dual-model aqueous Zn-CO2 batteries were realized by electrocatalysts capable of catalyzing CO2 reduction, water oxidation, and oxygen reduction. Concluding remarks include a summary of recent CO2 electrochemistry in metal-CO2 batteries and a brief discussion of future challenges and opportunities for practical aqueous Zn-CO2 batteries, such as highly reduced products and high production rate.

Reversible Aqueous Zinc-CO2 Batteries Based on CO2 -HCOOH Interconversion.

As a promising technique for CO2 fixation/utilization and energy conversion/storage, the metal-CO2 battery has been studied to improve its interconversion between CO2 and carbonates/oxalates. Herein, we propose and realize a reversible aqueous Zn-CO2 battery based on the reversible conversion between CO2 and liquid HCOOH on a bifunctional Pd cathode. The 3D porous Pd interconnected nanosheet with enriched edge and pore structure, has a highly electrochemical active surface to facilitate simultaneous selective CO2 reduction and HCOOH oxidation at low overpotentials. The resulting battery has a 1 V charge voltage, a cycling durability over 100 cycles, and a high energy efficiency of 81.2 %. The battery mechanism is proposed as Zn+CO2 +2 H+ +2 OH- ↔ ZnO+HCOOH+H2 O, through which the reversible conversion between CO2 and liquid HCOOH was realized.

Metal-Free Fluorine-Doped Carbon Electrocatalyst for CO2 Reduction Outcompeting Hydrogen Evolution.

The electrochemical CO2 reduction (ECDRR), as a key reaction in artificial photosynthesis to implement renewable energy conversion/storage, has been inhibited by the low efficiency and high costs of the electrocatalysts. Herein, we synthesize a fluorine-doped carbon (FC) catalyst by pyrolyzing commercial BP 2000 with a fluorine source, enabling a highly selective CO2 -to-CO conversion with a maximum Faradaic efficiency of 90 % at a low overpotential of 510 mV and a small Tafel slope of 81 mV dec-1 , outcompeting current metal-free catalysts. Moreover, the higher partial current density of CO and lower partial current density of H2 on FC relative to pristine carbon suggest an enhanced inherent activity towards ECDRR as well as a suppressed hydrogen evolution by fluorine doping. Fluorine doping activates the neighbor carbon atoms and facilitates the stabilization of the key intermediate COOH* on the fluorine-doped carbon material, which are also blocked for competing hydrogen evolution, resulting in superior CO2 -to-CO conversion.

CO2 Overall Splitting by a Bifunctional Metal-Free Electrocatalyst.

Photo/electrochemical CO2 splitting is impeded by the low cost-effective catalysts for key reactions: CO2 reduction (CDRR) and water oxidation. A porous silicon and nitrogen co-doped carbon (SiNC) nanomaterial by a facile pyrolyzation was developed as a metal-free bifunctional electrocatalyst. CO2 -to-CO and oxygen evolution (OER) partial current density under neutral conditions were enhanced by two orders of magnitude in the Tafel regime on SiNC relative to single-doped comparisons beyond their specific area gap. The photovoltaic-driven CO2 splitting device with SiNC electrodes imitating photosynthesis yielded an overall solar-to-chemical efficiency of advanced 12.5 % (by multiplying energy efficiency of CO2 splitting cell and photovoltaic device) at only 650 mV overpotential. Mechanism studies suggested the elastic electron structure of -Si(O)-C-N- unit in SiNC as the highly active site for CDRR and OER simultaneously by lowering the free energy of CDRR and OER intermediates adsorption.

Direct Solar-to-Electrochemical Energy Storage in a Functionalized Covalent Organic Framework.

A covalent organic framework integrating naphthalenediimide and triphenylamine units (NT-COF) is presented. Two-dimensional porous nanosheets are packed with a high specific surface area of 1276 m2 g-1 . Photo/electrochemical measurements reveal the ultrahigh efficient intramolecular charge transfer from the TPA to the NDI and the highly reversible electrochemical reaction in NT-COF. There is a synergetic effect in NT-COF between the reversible electrochemical reaction and intramolecular charge transfer with enhanced solar energy efficiency and an accelerated electrochemical reaction. This synergetic mechanism provides the key basis for direct solar-to-electrochemical energy conversion/storage. With the NT-COF as the cathode materials, a solar Li-ion battery is realized with decreased charge voltage (by 0.5 V), increased discharge voltage (by 0.5 V), and extra 38.7 % battery efficiency.

A multicomponent triformylphoroglucinol-based covalent organic framework for overall hydrogen peroxide photosynthesis.

A multicomponent covalent organic framework (COF-Tfp-BpyDaaq) integrating bipyridine with diaminoanthraquinone through a triformylphoroglucinol linkage was synthesized for the first time as a photocatalyst for overall H2O2 photosynthesis. It exhibits enhanced photo-charge separation and H2O2 production rate over its two-component counterparts, demonstrating the pivotal role of multicomponent synthesis in designing efficient photocatalysts.