Identification of the Active Sites on Metallic MoO2−x Nano-Sea-Urchin for Atmospheric CO2 Photoreduction Under UV,Visible, and Near-Infrared Light Illumination

We report an oxygen vacancy (V_o)-rich metallic MoO_2−x nano-sea-urchin with partially occupied band, which exhibits super CO₂ (even directly from the air) photoreduction performance under UV, visible and near-infrared (NIR) light illumination. The V_o-rich MoO_2−x nano-sea-urchin displays a CH₄ evolution rate of 12.2 and 5.8 μmol g_catalyst⁻¹ h⁻¹ under full spectrum and NIR light illumination in concentrated CO₂, which is ca. 7- and 10-fold higher than the V_o-poor MoO_2−x, respectively. More interestingly, the as-developed V_o-rich MoO_2−x nano-sea-urchin can even reduce CO₂ directly from the air with a CO evolution rate of 6.5 μmol g_catalyst⁻¹ h⁻¹ under NIR light illumination. Experiments together with theoretical calculations demonstrate that the oxygen vacancy in MoO_2−x can facilitate CO₂ adsorption/activation to generate *COOH as well as the subsequent protonation of *CO towards the formation of CH₄ because of the formation of a highly stable Mo−C−O−Mo intermediate.     

A “Pre-Division Metal Clusters” Strategy to Mediate Efficient Dual-Active Sites ORR Catalyst for Ultralong Rechargeable Zn-Air Battery

To conquer the bottleneck of sluggish kinetics in cathodic oxygen reduction reaction (ORR) of metal-air batteries, catalysts with dual-active centers have stood out. Here, a “pre-division metal clusters” strategy is firstly conceived to fabricate a N,S-dual doped honeycomb-like carbon matrix inlaid with CoN₄ sites and wrapped Co₂P nanoclusters as dual-active centers (Co₂P/CoN₄@NSC-500). A crystalline {Co^II ₂ } coordination cluster divided by periphery second organic layers is well-designed to realize delocalized dispersion before calcination. The optimal Co₂P/CoN₄@NSC-500 executes excellent 4e⁻ ORR activity surpassing the benchmark Pt/C. Theoretical calculation results reveal that the CoN₄ sites and Co₂P nanoclusters can synergistically quicken the formation of *OOH on Co sites. The rechargeable Zn-air battery (ZAB) assembled by Co₂P/CoN₄@NSC-500 delivers ultralong cycling stability over 1742 hours (3484 cycles) under 5 mA cm⁻² and can light up a 2.4 V LED bulb for ≈264 hours, evidencing the promising practical application potentials in portable devices.     

Electrical Pulse-Driven Periodic Self-Repair of Cu-Ni Tandem Catalyst for Efficient Ammonia Synthesis from Nitrate

Electrocatalytic nitrate reduction sustainably produces ammonia and alleviates water pollution, yet is still challenging due to the kinetic mismatch and hydrogen evolution competition. Cu/Cu₂O heterojunction is proven effective to break the rate-determining NO₃⁻-to-NO₂⁻ step for efficient NH₃ conversion, while it is unstable due to electrochemical reconstruction. Here we report a programmable pulsed electrolysis strategy to achieve reliable Cu/Cu₂O structure, where Cu is oxidized to CuO during oxidation pulse, then regenerating Cu/Cu₂O upon reduction. Alloying with Ni further modulates hydrogen adsorption, which transfers from Ni/Ni(OH)₂ to N-containing intermediates on Cu/Cu₂O, promoting NH₃ formation with a high NO₃⁻-to-NH₃ Faraday efficiency (88.0±1.6 %, pH 12) and NH₃ yield rate (583.6±2.4 μmol cm⁻² h⁻¹) under optimal pulsed conditions. This work provides new insights to in situ electrochemically regulate catalysts for NO₃⁻-to-NH₃ conversion.     

Bias-Free Solar-Driven Syngas Production: A Fe2O3 Photoanode Featuring Single-Atom Cobalt Integrated with a Silver-Palladium Cathode

Photoelectrochemical syngas production from aqueous CO₂ is a promising technique for carbon capture and utilization. Herein, we demonstrate the efficient and tunable syngas production by integrating a single-atom cobalt-catalyst-decorated α-Fe₂O₃ photoanode with a bimetallic Ag/Pd alloy cathode. A record syngas production activity of 81.9 μmol cm⁻² h⁻¹ (CO/H₂ ratio: ≈1 : 1) was achieved under artificial sunlight (AM 1.5 G) with an excellent durability. Systematic studies reveal that the Co single atoms effectively extract the holes from Fe₂O₃ photoanodes and serve as active sites for promoting oxygen evolution. Simultaneously, the Pd and Ag atoms in bimetallic cathodes selectively adsorb CO₂ and protons for facilitating CO production. Further incorporation with a photovoltaic, to allow solar light (>600 nm) to be utilized, yields a bias-free CO₂ reduction device with solar-to-CO and solar-to-H₂ conversion efficiencies up to 1.33 and 1.36 %, respectively.     

Inside Back Cover: Retina-Inspired Organic Photonic Synapses for Selective Detection of SWIR Light (Angew. Chem. Int. Ed. 6/2023)

Photonic synapses with the dual function of optical signal detection and information processing can simulate human visual system. However, photonic synapses with selective detection of short-wavelength infrared (SWIR) light have never been reported, which can not only broaden the human vision region but also integrate neuromorphic computation and infrared optical communication. Here, organic photonic synapses based on a new donor-acceptor copolymer P1 are fabricated, which exhibit excellent synaptic characteristics with selective detection for SWIR and extremely low energy consumption (2.85 fJ). The working mechanism is rooted in energy level barriers and unbalanced charge transportation. Moreover, these photonic synapses demonstrate excellent performance in multi-signal logic editing, letter imaging and memory with noise reduction function. This contribution provides ideas of constructing selective-response synapses for artificial visual system and neuromorphic computing.     

Electrocatalytically Activating and Reducing N2 Molecule by Tuning Activity of Local Hydrogen Radical

Decarbonizing N₂ conversion is particularly challenging, but essential for sustainable development of industry and agriculture. Herein, we achieve electrocatalytic activation/reduction of N₂ on X/Fe−N−C (X=Pd, Ir and Pt) dual-atom catalysts under ambient condition. We provide solid experimental evidence that local hydrogen radical (H*) generated on the X site of the X/Fe−N−C catalysts can participate in the activation/reduction of N₂ adsorbed on the Fe site. More importantly, we reveal that the reactivity of X/Fe−N−C catalysts for N₂ activation/reduction can be well adjusted by the activity of H* generated on the X site, i.e., the interaction between the X−H bond. Specifically, X/Fe−N−C catalyst with the weakest X−H bonding exhibits the highest H* activity, which is beneficial to the subsequent cleavage of X−H bond for N₂ hydrogenation. With the most active H*, the Pd/Fe dual-atom site promotes the turnover frequency of N₂ reduction by up to 10 times compared with the pristine Fe site.     

A Hydrazine-Nitrate Flow Battery Catalyzed by a Bimetallic RuCo Precatalyst for Wastewater Purification along with Simultaneous Generation of Ammonia and Electricity

The traditional technologies for industrial and agricultural effluent treatment are often energy-intensive. Herein, we suggest an electrochemical redox strategy for spontaneous and simultaneous decontamination of wastewater and generation of both fuels and electricity at low cost. Using hydrazine and nitrate effluents as a demonstration, we propose a hydrazine-nitrate flow battery (HNFB) that can efficiently purify the wastewater and meanwhile generate both ammonia fuel and electricity with the assistance of our developed bimetallic RuCo precatalyst. Specifically, the battery delivers a peak power density of 12 mW cm⁻² and continuously operates for 20 h with an ammonia yield rate of ca. 0.38 mmol h⁻¹ cm⁻² under 100 mA cm⁻². The generated electricity can further drive a hydrazine electrolyzer to produce hydrogen fuel. Our work provides an alternative pathway to purify wastewater and generate high value-added fuels at low cost.     

Inducing Covalent Atomic Interaction in Intermetallic Pt Alloy Nanocatalysts for High-Performance Fuel Cells

The harsh working environments of proton exchange membrane fuel cells (PEMFCs) pose huge challenges to the stability of Pt-based alloy catalysts. The widespread presence of metallic bonds with significantly delocalized electron distribution often lead to component segregation and rapid performance decay. Here we report L1₀−Pt₂CuGa intermetallic nanoparticles with a unique covalent atomic interaction between Pt−Ga as high-performance PEMFC cathode catalysts. The L1₀−Pt₂CuGa/C catalyst shows superb oxygen reduction reaction (ORR) activity and stability in fuel cell cathode (mass activity=0.57 A mg_Pt⁻¹ at 0.9 V, peak power density=2.60/1.24 W cm⁻² in H₂-O₂/air, 28 mV voltage loss at 0.8 A cm⁻² after 30 000 cycles). Theoretical calculations reveal the optimized adsorption of oxygen intermediates via the formed biaxial strain on L1₀−Pt₂CuGa surface, and the durability enhancement stems from the stronger Pt−M bonds than those in L1₁−PtCu resulted from Pt−Ga covalent interactions.     

Covalent Organic Frameworks for Energy Conversion in Photocatalysis

Intensifying energy crises and severe environmental issues have led to the discovery of renewable energy sources, sustainable energy conversion, and storage technologies. Photocatalysis is a green technology that converts eco-friendly solar energy into high-energy chemicals. Covalent organic frameworks (COFs) are porous materials constructed by covalent bonds that show promising potential for converting solar energy into chemicals owing to their pre-designable structures, high crystallinity, and porosity. Herein, we highlight recent progress in the synthesis of COF-based photocatalysts and their applications in water splitting, CO₂ reduction, and H₂O₂ production. The challenges and future opportunities for the rational design of COFs for advanced photocatalysts are discussed. This Review is expected to promote further development of COFs toward photocatalysis.     

Modulating Electronic Structures of Iron Clusters through Orbital Rehybridization by Adjacent Single Copper Sites for Efficient Oxygen Reduction

The atom-cluster interaction has recently been exploited as an effective way to increase the performance of metal-nitrogen-carbon catalysts for oxygen reduction reaction (ORR). However, the rational design of such catalysts and understanding their structure-property correlations remain a great challenge. Herein, we demonstrate that the introduction of adjacent metal (M)−N₄ single atoms (SAs) could significantly improve the ORR performance of a well-screened Fe atomic cluster (AC) catalyst by combining density functional theory (DFT) calculations and experimental analysis. The DFT studies suggest that the Cu−N₄ SAs act as a modulator to assist the O₂ adsorption and cleavage of O−O bond on the Fe AC active center, as well as optimize the release of OH* intermediates to accelerate the whole ORR kinetic. The depositing of Fe AC with Cu−N₄ SAs on nitrogen doped mesoporous carbon nanosheet are then constructed through a universal interfacial monomicelles assembly strategy. Consistent with theoretical predictions, the resultant catalyst exhibits an outstanding ORR performance with a half-wave potential of 0.92 eV in alkali and 0.80 eV in acid, as well as a high power density of 214.8 mW cm⁻² in zinc air battery. This work provides a novel strategy for precisely tuning the atomically dispersed poly-metallic centers for electrocatalysis.