Reversible Valence Research Articles

Aluminum ion chemistry of Na4Fe3(PO4)2(P2O7) for all-climate full Na-ion battery

Na4Fe3(PO4)2(P2O7) (NFPP) is currently drawing increased attention as a sodium-ion batteries (SIBs) cathode due to the cost-effective and NASICON-type structure features. Owing to the sluggish electron and Na+ conductivities, however, its real implementation is impeded by the grievous capacity decay and inferior rate capability. Herein, multivalent cation substituted microporous Na3.9Fe2.9Al0.1(PO4)2(P2O7) (NFAPP) with wide operation-temperature is elaborately designed through regulating structure/interface coupled electron/ion transport. Greatly, the derived Na vacancy and charge rearrangement induced by trivalent Al3+ substitution lower the ions diffusion barriers, thereby endowing faster electron transport and Na+ mobility. More importantly, the existing Al—O—P bonds strengthen the local environment and alleviate the volume vibration during (de)sodiation, enabling highly reversible valence variation and structural evolution. As a result, remarkable cyclability (over 10,000 loops), ultrafast rate capability (200 C), and exceptional all-climate stability (−40–60 °C) in half/full cells are demonstrated. Given this, the rational work might provide an actionable strategy to promote the electrochemical property of NFPP, thus unveiling the great application prospect of sodium iron mixed phosphate materials.

ZnS-embedded porous carbon for peroxydisulfate activation: Enhanced electron transfer for bisphenol A degradation

Transition metal sulfides have garnered increasing attention for their role in persulfate activation, a crucial process in environmental remediation. However, the function of metal sulfides without reversible valence changes, such as ZnS, remains largely unexplored in this context. Here we report ZnS-embedded porous carbon (ZnS-C), synthesized through the pyrolysis of Zn-MOF-74 and dibenzyl disulfide. ZnS-C demonstrates remarkable activity in activating peroxydisulfate (PDS) across a wide pH range, enabling the efficient mineralization removal of bisphenol A (BPA). Through electrochemical investigation and theoretical simulations of charge density distributions, we unveil that the electron transfer from BPA to PDS mediated by the ZnS-C catalyst governs the reaction. This study, both in theory and experiment, demonstrates metal sulfide as electron pump that enhances electron transfer efficiency in PDS activation. These findings redefine the role of metal sulfide catalysts, shedding new light on their potential for regulating reaction pathways in PDS activation processes.

The synergistic effect of Lewis acidic etching V4C3(MXene)@CuSe2/CoSe2 as an advanced cathode material for aluminum batteries

Herein, we focused on the development of the V4C3 MXene composite bimetallic selenide heterostructure (V4C3@CuSe2/CoSe2) as a cathode material for aluminum batteries. This heterostructure was prepared through a Lewis melt salt etching and selenization process. By capitalizing on the synergistic effect between the bimetallic selenide and V4C3 MXene, V4C3@CuSe2/CoSe2 exhibited rapid charge transfer and demonstrated superior discharge specific capacity compared to V4C3 composite monometallic selenide. Furthermore, the incorporation of V4C3 improved the material's stability during charging/discharging. The initial discharge specific capacity of V4C3@CuSe2/CoSe2 reached an impressive 809 mAh g–1 at 1 A g–1. Even after nearly 3000 cycles, it retained a substantial capacity of 169.1 mAh g–1. Ex-situ XPS analysis confirmed the reversible valence transitions of Cu, Co, and Se elements as the main energy storage reactions taking place in the cathode material. Density functional theory analysis provided further insights, revealing that the strong metallic behavior of the heterostructure stemmed from the charge rearrangement facilitated by the bimetallic selenide structure and the optimization of the energy level structure. Additionally, the presence of the bimetallic selenide structure significantly improved the adsorption efficiency of [AlCl4]–. Overall, this research contributes to the advancement of rechargeable aluminum ion batteries and presents a promising avenue for future developments in composite metal selenide structures and MXene-based materials.

Copper Tetraselenophosphate Cathode for Rechargeable Magnesium Batteries: A Redox-Active Polyatomic Anion Strategy to Design the Cathode Material

Rechargeable magnesium batteries attract interest as advantageous energy-storage devices, but the application is being hampered by the deficiency of suitable cathodes. The traditional method to weaken the interaction between bivalent Mg2+ cations and the cathode material is to increase the anion radius, but excessive expansion of the anion would lead to a decrease of the theoretical capacity and offset the performance improvement. Herein, a new strategy using a redox-active polyatomic anion is developed in terms of copper tetraselenophosphate (Cu3PSe4) fabricated by the PSe43– anion. The covalent P–Se bond facilitates the negative charge delocalization of the PSe43– anion and weakens the interaction with Mg2+ cations, which result in rapid solid-phase Mg2+ diffusion kinetics. The PSe43– anion also provides extra capacities by reversible valence state change of the P element. Cu3PSe4 delivers a high Mg-storage capacity of 225 mAh g–1 at 50 mA g–1 and a superior rate performance of 62 mAh g–1 at 5000 mA g–1, as well as a stable cyclability of 500 cycles. The redox-active polyatomic anion strategy herein opens a new avenue for the exploration of magnesium battery cathodes with a comprehensive consideration of kinetic performance and theoretical capacity.

3D nanothorn cluster-like Zn-Bi2S3 sensitized WO3/ZnO multijunction with electron-storage characteristic and adjustable energy band for improving sustained photoinduced cathodic protection application

Solar energy-driven photoinduced cathodic protection (PICP) technology utilizes solar energy to protect marine metallic structures against severe marine corrosion. To enhance the solar energy utilization and strengthen dark-state application for realizing long-term protection, herein, a 3D nanothorn cluster-like WO3/ZnO/Zn-Bi2S3 multijunction with electron-storage characteristic and adjustable energy band was constructed. It exhibited an enhanced continuous release of photogenerated electron and sustained cathodic protection in dark conditions. Exposed to only 100 s of simulated sunlight irradiation, the WO3/ZnO/Zn-Bi2S3could store 5.27×10−2 C electrons and provide up to 5460 s of sustained CP for the coupled metal after light stops, which was 10.8 and 3.5 times higher than those of WO3/ZnO (4.89×10−3 C) and WO3/Zn-Bi2S3 (1.51×10−2 C), respectively. The WO3 nanothorn cluster-like substrate with reversible valence transformation of W6+/W5+ together with the large surface area and one-dimensional transmission path can store photogenerated electrons under illumination and release photogenerated electrons after light stops efficiently. Notably, the tri-phase heterojunction with introduction of intermediate “Carrier Springboard” ZnO between WO3 and Zn-Bi2S3 contributed to the building of well-matched energy band gradient to strengthen the directional backward transfer of photogenerated electrons and holes. The energy band of Bi2S3 sensitizer was adjusted towards negative direction by doping with zinc element to boost PICP application performance. The reversible valence transformation of Bi3+/Bi5+ could promote the consumption of photogenerated holes. These synergistically enhanced the sustained PICP performance of the WO3/ZnO/Zn-Bi2S3 photoelectrode both in dark and light conditions. This design shed light on energy-storage photoelectrodes for long-term PICP of metallic materials.

Metal-Free Carbon-Based Covalent Organic Frameworks with Heteroatom-Free Units Boost Efficient Oxygen Reduction.

Accurate identification of carbon-based metal-free electrocatalyst (CMFE) activity and enhancing their catalytic efficiency for O2 conversion is an urgent and challenging task. This study reports a promising strategy to simultaneously develop a series of covalent organic frameworks (COFs) with well-defined heterocyclic-free biphenyl or fluorenyl units. Unlike heteroatom doping, the developed method not only supplies methyl-induced molecular configuration to promote activity, but also provides a direct opportunity to identify heteroatom-free carbon active centers. The introduction of methyl groups (MGs) with reversible valence bonds into a pristine biphenyl-based COF results in an excellent performance with a half-wave potential of 0.74V versus the reversible hydrogen electrode (RHE), which is among the highest values for CMFE-COFs as oxygen reduction reaction (ORR) electrocatalysts. Combined with in situ Raman spectra and theoretical calculations, the MG-bound skeleton (DAF-COF) is found to produce ortho activation, confirming the ortho carbon (site-5) adjacent to MGs as active centers. This may be attributed to the opening and binding of MGs, which effectively regulate the molecular configuration and charge redistribution, as well as improve charge transfer and reduce the energy barrier. This study provides insight into the design of highly efficient metal-free organic electrocatalysts via the regulation of valence bonds.

A Sonication‐Activated Valence‐Variable Sono‐Sensitizer/Catalyst for Autography Inhibition/Ferroptosis‐Induced Tumor Nanotherapy

The effective deployment of reactive oxygen species (ROS)-mediated oncotherapy in practice remains challenging, mired by uncontrollable catalytic processes, stern reaction conditions and safety concerns. Herein, we develop a copper nanodot integrating sonodynamic and catalytic effects within one active center, which responds to exogenous ultrasound (US) and endogenous H2O2 stimuli. US irradiation induces the valence conversion from CuII to CuI catalyzing H2O2 into ⋅OH for chemodynamic therapy. Meanwhile, valence transformation results in electron-hole pairs separation, promoting ROS generation for sonodynamic therapy. Notably, copper nanodots not only block lysosome fusion and degradation leading to autophagy flux blockage, but also interfere with the glutathione peroxidase 4 and cystine-glutamate antiporter SLC7A11 function achieving ferroptosis. Furthermore, reversible valence changes, inherent hydrophilicity and renal clearance ultrasmall size guarantee biosafety.

A Sonication-Activated Valence-Variable Sono-Sensitizer/Catalyst for Autography Inhibition/Ferroptosis-Induced Tumor Nanotherapy.

The effective deployment of reactive oxygen species (ROS)-mediated oncotherapy in practice remains challenging, mired by uncontrollable catalytic processes, stern reaction conditions and safety concerns. Herein, we develop a copper nanodot integrating sonodynamic and catalytic effects within one active center, which responds to exogenous ultrasound (US) and endogenous H2 O2 stimuli. US irradiation induces the valence conversion from CuII to CuI catalyzing H2 O2 into ⋅OH for chemodynamic therapy. Meanwhile, valence transformation results in electron-hole pairs separation, promoting ROS generation for sonodynamic therapy. Notably, copper nanodots not only block lysosome fusion and degradation leading to autophagy flux blockage, but also interfere with the glutathione peroxidase 4 and cystine-glutamate antiporter SLC7A11 function achieving ferroptosis. Furthermore, reversible valence changes, inherent hydrophilicity and renal clearance ultrasmall size guarantee biosafety.

Hexagonal NaxWO3 nanocrystals with reversible valence states for microwave thermal and chemodynamic combined cancer therapy

Microwave ablation (MWA) is recognized as the mainstream choice for tumor thermal ablation, but the rapid diffusion of heat and high tumor recurrence rate are still the primary bottlenecks in the clinic application of MWA. Hexagonal tungsten oxide nanomaterials could be potentially exploited as microwave sensitizers to elevate MWA efficacy due to the inherent tunnel structure and ions intercalation characteristics. Importantly, the flexible redox states of W element make it promising candidates for chemodynamic therapy (CDT) to further improve microwave-mediated cancer treatment. Herein, multifunctional hexagonal phase NaxWO3 nanocrystals modified with polyvinylpyrrolidone are prepared. Such NaxWO3 nanocrystals could not only function as microwave sensitizers to produce microwave heating effects for cancer cell killing, but also act as nano-catalyst to decompose hydrogen peroxide into highly oxidative hydroxyl radicals and simultaneously consume intracellular glutathione for an enhanced CDT effect. In addition, the hyperthermia generated by microwave irradiation could further upgrade the efficacy of CDT, achieving a combined effect of MWA and heat-amplified CDT. Notably, NaxWO3 nanocrystals enable the effective destruction of tumor tissues under microwave irradiation without inducing significant side effects to normal tissues. Consequently, our findings propose an innovative and safe nanotechnology strategy to reinforce the therapeutic outcome of MWA and CDT.

Two-Dimensional Beidellite/Carbon Superlattice for Boosting Lithium-Ion Storage Performance.

Two-dimensional Fe-beidellite/carbon (Fe-BEI@C) superlattice-like heterostructure was prepared by intercalation of glucose in the gallery of layered Fe-BEI followed by calcination. The interlaminar and superficial carbon coating enables Fe-BEI to have good rate performance, fast lithium-ion diffusion, and high pseudocapacitance contribution, leading to excellent lithium storage performance as anode material for lithium-ion batteries (LIBs). The Fe-BEI@C/Li half cell delivers a maximum specific capacity of 850 mAh·g-1 at 0.5 A·g-1 and has a 92.3% retention rate after 100 cycles along with a high-rate performance of 403 mAh·g-1 at 5 A·g-1. The reversible valence state change of Si2+/Si4+ and Fe0/Fex+ (0 < x < 3) in electrochemical cycles are realized without collapse of layered structure. Additionally, the Fe-BEI@C heterostructure displays a high Li+ diffusion coefficient of 10-13∼10-10 cm2 s-1, illustrating fast Li+ transfer in the interlayer of Fe-BEI@C heterostructure. Dynamic analysis reveals that the Si redox reaction is almost dominated by surface control and that of Fe is mainly diffusion-controlled. This work has exploited a novel layered silicate as anode material for LIBs and developed a molecular-level carbon hybridization method to improve their electrochemical performance, which is meaningful for the application of layered silicate in the energy-storage field.

Reversible Mn valence state switching in submicron α-Al2O3:Mn by soft X-rays and blue light - a potential pathway towards multilevel optical data storage.

The generation of Mn4+ in α-Al2O3:Mn3+ by soft X-ray exposure is demonstrated with a large dynamic range of the X-ray generated Mn4+ luminescence signal, indicating the potential use of α-Al2O3:Mn3+ for multilevel optical data storage. Samples with a range of Mn concentrations (0.05, 0.1, 0.2, 0.4, 0.6 and 1.2 atom%) were prepared via a facile combustion method and the sample with 0.4 atom% was found to display the highest luminescence intensity. The stored information can be read out via the R-lines (2E → 4A2) under ∼470 nm (4A2 → 4T2), or ∼630 nm (4A2 → 2T1) excitation with the latter being preferred since photobleaching is minimized. Interestingly, the Mn4+ valence state can be fully switched back to Mn3+ by blue light exposure (e.g., 462 nm laser diode). The stored information could be repeatedly written and erased, showing no significant deterioration over five consecutive cycles, with less than 5% uncertainty.

High-Performance Catalytic Four-Channel Hollow Fibers with Highly Dispersed Nickel Nanoparticles Prepared by Atomic Layer Deposition for Dry Reforming of Methane

Highly dispersed nickel (Ni) nanoparticles (NPs) with an average particle size of 4.3 nm were uniformly deposited on the outer surface, the inner channel surface, and inside the pores of 20 cm long four-channel α-Al2O3 hollow fibers (HFs) by atomic layer deposition (ALD) for dry reforming of methane (DRM). Cerium oxide (CeO2) was added to promote the catalytic performance of Ni/Al2O3–HF catalysts. Rationally designed filling methods, by tuning the reactor size and inert fillings, can reduce the catalyst bed voidage in a fixed bed reactor for better reactant gas distribution, effectively utilize the Ni reactive sites, and achieve excellent catalytic performance. It was found that the CeO2-promoted Ni/Al2O3–HF catalyst was highly active and highly stable without deactivation during an overall 400-h DRM test at 850 °C. CeO2 with reversible valence states could participate in surface reactions; especially, the formation of CeAlO3 provided sufficient surface Ce3+ for CO2 activation and enhanced the stability and reusability of the HF catalysts.

Synthesis and application of self-healing elastomers with high healing efficiency and mechical properties based on multi-healing systems

A novel self-healing polyurethane elastomer based on multi-healing systems is presented. In addition, the flexible sensor made of above elastomers doped with conductive graphene can respond to external force quickly and stably. Intrinsic self-healing materials designed by combining reversible valence bonds or ionic coordination have attracted much attention due to their ability to recover from mechanical damage. However, their mechanical properties tend to deteriorate due to the increased rigidity of the chain. In this work, we report a self-healing polyurethane elastomer with multiple healing systems. 3,3′-dithiodipropionic acid (TDPA) and iron ion-2,6-diaminopyridine (DAP) were used as dynamic chain extenders and ionic ligands, respectively. They can be effectively unsealed at a certain temperature to ensure that the self-healing efficiency is not affected by the material formula. By changing the content of hard and soft segments, the mechanical properties and self-healing properties of the material can be adjusted in a large range. When the molar ratio of TDPA and DAP is 0.5:0.5, the polyurethane based on multiple healing system only needs to be healed at 70 °C for 12 h, and the self-healing efficiency can reach 93.48%. The structural rigidity and high reversibility of metal complexing agent DAP and iron ions play an important role in enhancing mechanical strength and maintaining self-healing efficiency at 70 °C. Based on the above research, we prepared the strain sensor by combining self-healing polyurethane and conductive graphene. The sensor can respond to external force quickly and stably. This work provides a feasible strategy for the preparation of mechanically robust polyurethane elastomers and self-healing flexible stress sensors with high self-healing efficiency at 70 °C.

Natural Kaolin-Based Ni Catalysts for CO2 Methanation: On the Effect of Ce Enhancement and Microwave-Assisted Hydrothermal Synthesis.

Natural kaolin-based Ni catalysts have been developed for low-temperature CO2 methanation. The catalysts were prepared via a one-step co-impregnation of Ni and Ce onto a natural kaolin-derived metakaolin using a microwave-assisted hydrothermal method as an acid-/base-free synthesis method. The influences of microwave irradiation and Ce promotion on the catalytic enhancement including the CO2 conversion, CH4 selectivity, and CH4 yield were experimentally investigated by a catalytic test of as-prepared catalysts in a fixed-bed tubular reactor. The relationship between the catalyst properties and its methanation activities was revealed by various characterization techniques including X-ray fluorescence, X-ray diffraction, Brunauer–Emmett–Teller, scanning electron microscopy, selected area electron diffraction, transmission electron microscopy, elemental mapping, H2 temperature-programmed reduction, and X-ray absorption near-edge structure analyses. Among the two enhancement methods, microwave and Ce promotion, the microwave-assisted synthesis could produce a catalyst containing highly dispersed Ni particles with a smaller Ni crystallite size and higher catalyst reducibility, resulting in a higher CO2 conversion from 1.6 to 7.5% and a better CH4 selectivity from 76.3 to 79.9% at 300 °C. Meanwhile, the enhancement by Ce addition exhibited a great improvement on the catalyst activities. It was experimentally found that the CO2 conversion increased approximately 7-fold from 7.5 to 52.9%, while the CH4 selectivity significantly improved from 79.9 to 98.0% at 300 °C. Though the microwave-assisted synthesis could further improve the catalyst activities of Ce-promoted catalysts, the Ce addition exhibited a more prominent impact than the microwave enhancement. Cerium oxide (CeO2) improved the catalyst activities through mechanisms of higher CO2 adsorption capacity with its basic sites and the unique structure of CeO2 with a reversible valence change of Ce4+ and Ce3+ and high oxygen vacancies. However, it was found that the catalyst prepared by microwave-assisted synthesis and Ce promotion proved to be the optimum catalyst in this study. Therefore, the present work demonstrated the potential to synthesize a nickel-based catalyst with improved catalytic activities by adding a small amount of Ce as a catalytic promoter and employing microwave irradiation for improving the Ni dispersion.

Atomic-scale investigation of Lithiation/Delithiation mechanism in High-entropy spinel oxide with superior electrochemical performance

• The cycling microstructure evolution of spinel (CrMnFeCoNi) 3 O 4 HEO was precisely demonstrated at atomic scale. • The detailed information of HEO cycling electrochemistry was firstly revealed by EELS. • The lithiated nano grains enhanced the diffusion mobility of spinel oxides and Mn, contributing to the reversible capacity. • The in-depth understanding of the fundamental science influences future development of HEOs in lithium energy storage systems. Transition-metal high-entropy oxides (HEOs) are promising electrode materials for lithium-ion batteries (LIBs) due to their superior electrochemical properties and excellent long-term cycling stability. The performance of HEOs for LIBs is highly correlated with their microstructures, especially their evolution during charging/discharging. However, there is limited information regarding this topic in the literature. In this study, the unique transition behavior of a spinel HEO, (CrMnFeCoNi) 3 O 4 , at various states of charge and cycle numbers is examined in detail for the first time. Although the elemental segregation of lithiated HEO particles is observed, the crystal structure remains spinel, leading to great cyclability. Mn nanocrystals form at 0.5 V lithiation and metallic Cr, Fe, Ni, and Co particles form at 0.01 V lithiation. The spinel Cr x Fe 3-x O 4 and LiNi x Co 1-x O 2 phases act as seeds that grow by devouring surrounding metal nanoparticles during delithiation. The Mn can reversibly move at least dozens of nanometers across the oxide during lithiation/delithiation. The detailed cycling mechanism is examined using electron energy-loss spectroscopy. The reversible valence state variations of the constituent elements are observed. The results provide an in-depth understanding of the fundamental lithiation/delithiation mechanism of HEO, which will facilitate the development of better multi-element HEOs for Li + storage applications.

Green synthesis of CoWO4 powders using agar-agar from red seaweed (Rhodophyta): Structure, magnetic properties and battery-like behavior

This work reports a proteic sol-gel green method that uses agar-agar from red seaweed (Rhodophyta) for synthesizing cobalt tungstate (CoWO4) powders for battery-like electrodes. For comparison, CoWO4 is also prepared by a similar proteic chemical route that uses flavorless gelatin. The as-prepared powders were calcined at 800 °C for 2 h and further characterized by XRD (with Rietveld refinement), SEM/EDS, FTIR/Raman/UV–Vis–NIR spectroscopies, VSM, and various electrochemical techniques for assessing the battery-like behavior in alkaline media (3 M KOH). The results indicate that samples produced by gelatin show average particle size of 150 nm and crystallite size of 68 nm, against 284 nm (particle) and 84 nm (crystallite) for agar-agar processed materials. Magnetic assessment at 300 K showed a paramagnetic behavior for both samples. The analysis of these curves showed an effective magnetic moment per cobalt atom of 4.908 μB and 4.926 μB for samples prepared using gelatin and agar-agar, respectively. The performance of CoWO4 as battery-like electrodes is ascribed due to a surface faradaic redox reaction mechanism related to reversible valence state between Co2+ and Co3+. Discharging curves indicate no substantial difference of electrochemical performance, with maximum specific capacity of 77 C g−1 at a specific current of 1 A g−1. The long-term stability of electrodes is confirmed by a capacity retention of around 98% over 1000 charge-discharge cycles at 1 A g−1.

Oscillation of Work Function during Reducible Metal Oxide Catalysis and Correlation with the Activity Property

AbstractDeducing from the fact that RMO catalysis typically involves reversible valence states transformation of active sites, we report one new model that uses RMO work function and its oscillation as descriptors to depict the activity property. Our experiments and DFT simulations of CO oxidation model reaction lead to an inverted volcano correlation between the two descriptors and the activity energy barrier, which shows good consistence with this new model and thus validates its effectiveness. The findings of work function and the oscillation as governing structural parameters provide a plausible theory to understand RMO catalysis and guide the catalyst research.

Recent In Situ/Operando Spectroscopy Studies of Heterogeneous Catalysis with Reducible Metal Oxides as Supports

For heterogeneous catalysis, the metal catalysts supported on reducible metal oxides, especially CeO2 and TiO2, have long been a research focus because of their excellent catalytic performance in a variety of catalytic reactions. Detailed understanding of the promotion effect of reducible metal oxides on catalytic reactions is beneficial to the rational design of new catalysts. The important catalytic roles of reducible metal oxides are attributed to their intimate interactions with the supported metals (e.g., strong metal-support interaction, electronic metal-support interaction) and unique support structures (e.g., oxygen vacancy, reversible valence change, surface hydroxyl). However, the structures of the catalysts and reaction mechanisms are strongly affected by environmental conditions. For this reason, in situ/operando spectroscopy studies under working conditions are necessary to obtain accurate information about the structure-activity relationship. In this review, the recent applications of the in situ/operando spectroscopy methodology on metal catalysts with reducible metal oxides as supports are summarized.

Synthesis of 2-phenyl-1,3-di(4-pyridyl)naphthvalene by photoinduced reversible valence isomerization of 2-phenyl-1,3-di(4-pyridyl)naphthalene

2-Phenyl-1,3-di(4-pyridyl)naphthvalene 3a was synthesized by the photoinduced reversible valence isomerization of 2-phenyl-1,3-di(4-pyridyl)naphthalene 2a. Then, 3a was converted into 3-phenyl-1,2-di(4-pyridyl)naphthalene 4a and 2a simultaneously. The t1/2 of 3a in DMSO-d6 at 90 °C was 2 h, while that at 110 °C was approximately 10 min.

Reversible and cooperative photoactivation of single-atom Cu/TiO2 photocatalysts.

The reversible and cooperative activation process, which includes electron transfer from surrounding redox mediators, the reversible valence change of cofactors and macroscopic functional/structural change, is one of the most important characteristics of biological enzymes, and has frequently been used in the design of homogeneous catalysts. However, there are virtually no reports on industrially important heterogeneous catalysts with these enzyme-like characteristics. Here, we report on the design and synthesis of highly active TiO2 photocatalysts incorporating site-specific single copper atoms (Cu/TiO2) that exhibit a reversible and cooperative photoactivation process. Our atomic-level design and synthetic strategy provide a platform that facilitates valence control of co-catalyst copper atoms, reversible modulation of the macroscopic optoelectronic properties of TiO2 and enhancement of photocatalytic hydrogen generation activity, extending the boundaries of conventional heterogeneous catalysts.