Costate Research Articles

Mass minimization of an Euler-Bernoulli beam with coupled bending and axial vibrations at prescribed fundamental frequency

The problem of determining the optimum shape of a homogeneous Euler–Bernoulli beam of a circular cross-section, in which the coupled axial and bending vibrations arose due to complex boundary conditions, is considered. The beam mass is minimized at prescribed fundamental frequency. The problem is solved applying Pontryagin’s maximum principle, with the beam cross-sectional diameter derivative with respect to longitudinal coordinate taken for control variable. This problem involves first-order singular optimal control, the calculations of which allowed the application of the Poisson bracket formalism and the fulfillment of the Kelley necessary condition on singular segments. Numerical solution of the two-point boundary value problem is obtained by the shooting method. An inequality constraint is imposed to the beam diameter derivative. Depending on the size of the diameter derivative boundaries, the obtained solutions are singular along the entire beam or consist of singular and non-singular segments, where the diameter derivative is at one of its boundaries. It is shown that such system is self-adjoint, so that only one differential equation of the costate equations system was integrated and the rest costate variables were expressed via the state variables. Also, the paper shows the fulfillment of necessary conditions for the optimality of junctions between singular and non-singular segments, as well as the percent saving of the beam mass compared to the beams of constant diameter at identical value of the fundamental frequency.

Study of photoionization mass spectrum of carbon monoxide from ionization threshold to 575 Å by using synchrotron radiation

The vacuum-ultraviolet photoionization efficiency spectroscopy (PIES) of carbon monoxide in a region 575–890 Å has been investigated with time-of-flight (TOF) photoionization mass spectrometry (PIMS) by using tunable synchrotron radiation (SR). Three photoionization thresholds were determined to be 14.015, 16.550 eV and 19.670 eV for the X2Σ+, A2Π and B2Σ+ states of CO+, respectively, which are in very good agreement with those of previous investigation. Furthermore, the Rydberg series converging to the X2Σ+, A2Π, B2Σ+, D2Π and C2Σ+ states of CO+ were assigned clearly, according to the PIES of CO and calculation with Rydberg series formula. In particular, the Rydberg series (RX-I) (ν+ = 2, 3 and 4) and RX-TTI series (ν+ = 1, 2, 3 and 4) converging to CO+ (X2Σ+), the Rydberg series (RB-V) (ν+ = 1, 2 and 3) converging to CO+ (B2Σ+), and a new vibrational progression (n = 2) converging to CO+ (A2Π) were all identified and listed for the first time. Generally speaking, the Rydberg series identified in this work are in good accordance with those of previous study. Moreover, some of them are extended to higher number, and some new members are classified for the first time.

A reaction mechanism for vibrationally-cold low-pressure CO2 plasmas

The use of plasmas for CO2 utilization has been under investigation in recent years following a wave of environmental awareness. In this work, previously published experimental results on vibrationally cold CO2 plasmas are modelled to define a reaction mechanism, i.e. a set of reactions and rate coefficients validated against benchmark experiments. The model couples self-consistently the electron and heavy particle kinetics. In turn, the simulated results are validated against measurements taken in CO2 DC glow discharges in a relatively large range of experimental conditions: at pressures from 0.4 to 5 Torr, reduced electric fields ranging from 50 to 100 Td and gas flowing from 2 to 8 sccm. The model predicts the measured values of product formation (CO and O) as well as discharge power and electric field. After validation, a thorough analysis of the model’s results is presented, including: electron properties, species densities, power distribution into different excitation channels and main creation and destruction mechanisms of the main species. It is shown that, although vibrational populations are low, they have a significant effect on the electron properties and thus on the electric field and conversion. Moreover, the shape of the EEDF is significantly dependent on the dissociation degree. The role of electronically excited states on CO2 dissociation is also analyzed, showing that the first electronic excited state of CO can have a beneficial or detrimental effect in further producing CO and O in the discharge.

A Molecular Crystal Shows Multiple Correlated Magnetic and Ferroelectric Switchings

Simultaneous control of the magnetic and electric properties of materials is crucial for their application in next-generation memory and sensor devices. Herein, we report a single-crystal Co(II) co...

S Doping Optimized Intermediate Energetics of FeCoOOh for Enhanced Oxygen Evolution Catalytic Activity

Transition metal sulfides have been demonstrated to be more active electrocatalysts than the corresponding (hydr)oxides for oxygen evolution reaction (OER). The nature of active sites, however, remains unclear. Herein, we study whether S could promote the OER activity of FeCoOOH and try to identify the catalytically active centers. Density functional theory suggests that two coordinating S could work synergistically with one adjacent Fe to optimize the electronic states of Co, resulting in decreased binding energy of OH* (ΔEOH) while little changed ΔEOH, and thus significantly lowering the catalytic overpotential. Further experimental studies validate the synergistic effect between S and Fe on tuning the electronic structure and the greatly improved catalytic activity with a small overpotential of 205.4 mV to drive 20 mA cm-2. This study unveils the origin of the high catalytic activity of transition metal sulfides and provides insights into the design of efficient OER electrocatalysts.

Influence of Oxygen Vacancy on Pseudocapacitance of La0.8Sr0.2CoO3-δ

Since the discovery of the charge storage mechanism involving a charge compensation by anion that can happen for some pseudocapacitive materials, oxides from the perovskite family have been intensively studied during the past five years, such as LaMO3-δ (M = Mn, Fe, Co, Ni). The oxygen vacancy present in some perovskites naturally becomes the center of this new mechanism. Indeed, the vacancies are suggested to host oxygen/hydroxyl ions to compensate the oxidation of the transition metal, and to release these ions during the reduction. Interestingly, there has not been any report dedicated to reveal the correlation between the oxygen vacancy with the pseudocapacitance of these materials.We propose here the study of the influence of the oxygen stoichiometry of the perovskite La0.8Sr0.2CoO3-δ, written as LSC82, used as pseudocapacitive electrode material. LSC82 has been prepared by a urea-nitrate combustion method, and then calcined at 850°C. Materials having different oxygen stoichiometries were obtained by different cooling rates. Electrochemical tests were performed on LSC82 based electrodes in 5M LiNO3 electrolyte to reveal the correlation between the oxygen stoichiometry and pseudocapacitve performance. The oxidation states of Co and the oxygen vacancies content in the various prepared LSC82 have been determined by various technics such iodometric titration, X-ray Absorption Spectroscopy and X-ray Photoelectron Spectroscopy. By associating electrochemical tests with spectroscopic technics, it is possible to connect oxygen vacancies content with electrochemical performances.Understanding the role of oxygen vacancies could give new lead to improving the performances of such materials.

(Invited) Towards Solving the Long Standing Mystery of the Chemical State of Co in PtxCo1-X to Boost HOR and ORR

Recently, Pt-based core-shell nanoparticles (NPs) have emerged as highly active catalyst materials to accelerate the sluggish oxygen reduction reaction (ORR) in acidic media as well as the hydrogen oxidation reaction (HOR) in alkaline. Less attention has been payed to the chemical state of the less noble metal after forming core-shell NPs. Intuitively; a metallic state of the less noble metal inside the particles has been suggested from many research groups.In this talk, we will show a new catalyst concept for Pt-Co nanoparticles by manipulating the surface arrangement and composition induced by the reaction conditions. More precisely, our catalysts exhibit superior Pt surface area-based specific activities (up to 10-fold) and Pt mass-based activities (up to 5-fold) towards the ORR compared to commercial Pt/C at 0.95 VRHE. In addition, we will show the influence of the chemical state and surface enrichment of the cobalt on the HOR activity in alkaline media.Altogether, we will solve the long standing mystery of the chemical state of the cobalt and its distribution for PtxCo1-x nanoparticles and its remarkable effect on the catalytic performance for HOR and ORR.

Effect of Cobalt Content on Charge Compensation Mechanism of LiNixMnyCozO2 Cathode for Lithium Ion Battery

LiCoO2 (LCO) is commonly used as a cathode for Li-ion batteries (LiBs) owing to its excellent intercalation nature, high voltage, and cyclic performance [1, 2]. However, LCO has issues due to the potential risk of future price increases of Co [3, 4]. Many efforts have been made to reduce the amount of Co in the cathode by replacing it with Ni and/or Mn, and LiNixMnyCozO2 (NMC) has been developed. NMC622, which contains 60 mol % of Ni in the transition metal composition, is now adopted in the majority of the electric vehicle battery chemistry. Although Ni-rich NMC is a promising alternative to low-Co cathodes, it is not clear whether the amount of Co can be further reduced from the present NMC622 without degrading cyclic stability. To further reduce the amount of Co, it is necessary to clarify the role of Co in the charge compensation mechanism and replace it with alternative elements with functions similar to those of Co.In this study, we conducted XAFS, XRD and first-principles calculations for the NMC cathode with various transition metal composition ratios to clarify that the roles of Co, Ni, Mn, and O in the charge compensation mechanism. Synchrotron X-ray experiments were performed at SPring-8 and NewSUBARU synchrotron radiation facility in Japan. The first-principles calculations were carried out with Vienna Ab-initio Simulation Package (VASP) [5, 6], which uses plane-wave basis sets.Fig. 1 shows the oxygen K-edge XANES spectra collected by the partial fluorescence yield (PFY) method at different states of charge (SOCs). As for the LCO, the peak intensity around 528 eV changed along with the SOC, suggesting that oxygen contributes to the charge compensation. Similar spectral changes were also observed with NMC111, NMC622, and slightly with NMC 811. In contrast, the white line energy in the Co L3-edge absorption hardly changed at any transition metal composition. Although there are various theories about the role of Co and oxygen in the charge compensation [7], our results show that there is no obvious change in the charge state of Co and oxygen contributes the most to the charge compensation in the LCO system. Detailed analysis including first-principles calculations will be discussed at the meeting.[1] K. Mizushima et al., Mater. Res. Bull. 15, 783 (1980).[2] A. Du Pasquier et al., J. Power Sources 115, 171 (2003).[3] P.A. Nelson et al., Modeling the Performance and Cost of Lithium-Ion Batteries for Electric-Drive Vehicles, Argonne National Laboratory, 2012.[4] Elsa A. Olivetti e t al., Joule 1, 229 (2017).[5] P. E. Blöch, Phys. Rev. B 50, 17953 (1994).[6] G. Kresse et al., Phys. Rev. B 59, 1758 (1999).[7] B. Li et al., Adv. Mater. 29, 1701054 (2017) Figure 1

Kendali Optimal Model LCS Pada Populasi Tanaman Padi Sawah Dari Serangan Hama Tikus Sawah Dan WBC Menggunakan Prinsip Minimum Pontryagin

ABSTRACT
 Rice field plants (Oryza sativa) is one of the main food crop that very essential for common poeple. On the other hand, rice become as the main commodity of the common poeple. According to Badan Pusat Statistik ( BPS ) data, the consumption of it in 2011 reached 139 kg of due to 237 million of Indonesian resident. The cultivation of rice field production obstacle is the pest attack. The able prime pest that caused the rice production damage is field mouse pest (Rattus argintiventer) and rice stem pest (Nilaparvata Lugens). Both types have a very high reproduction rate. This research studies mathematically the damage of rice field plants population control at vegetative phase. That designed to minimize the number of vegetative rice population phase. A logistic Competing Species model is built to describe the interaction between both the pest at the vegetative phase rice growth. The Pontryagin minimum principles is used to determine the optimal control solution. The solution is solved from the state and co-state equation that stationery evaluated using the indexed performance with optimal control and . The research result of indicate that the optimal control just optimalize the vegetative rice phase damage while the pest is not optimalized yet.
 Keyword : Stability, Jacoby Matrix, Eigen Value, Pontryagin Minimum, Oryza Sativa, Rattus Argintivente, Nilaparvata Lugens

Topotactically Transformed Polygonal Mesopores on Ternary Layered Double Hydroxides Exposing Under-Coordinated Metal Centers for Accelerated Water Dissociation.

Layered double hydroxides (LDHs) have been recognized as potent electrocatalysts for oxygen evolution reaction (OER), but are lacking in hydrogen evolution reaction (HER) activities due to the sluggish kinetics of water dissociation in alkaline medium. Herein, aiming to simultaneously bolster the HER and OER kinetics, a metal-organic framework (MOF) mediated topotactic transformation tactic is deployed to fabricate holey ternary CoFeNi LDHs on nickel foam, exposing polygonal mesopores with atomistic edge steps and lattice defects. The optimized catalyst requires only an external voltage of 1.49V to afford the water splitting current density of 10mA cm-2 apart from the superb electrolytic stability, far surpassing the benchmark Pt/C||RuO2 couple. More importantly, mechanistic investigations utilizing advanced spectroscopies in conjunction with density function theory (DFT) understandings unravel while the synergetic effect among under-coordinated metal centers lowers the energy barrier of water dissociation, Fe-doping enables further modulating the d-band density of states (DOS) of Co and Ni in favor of intermediates binding, thereby promoting the intrinsic HER activity. Operando Raman studies reveal negligible structural change of the LDHs during the HER process, whereas for OER the active sites can quickly turn into oxyhydroxides in the presence of lattice defects and under-coordinated metal centers.

Dielectric and magnetic properties, NEXAFS spectroscopy of Co-doped of multicomponent bismuth niobate pyrochlore

Two series of Bi2Mg1-xCoxNb2O9 and Bi2MgNb2-2xCo2xO9-δ preparations with pyrochlore structure were synthesized using solid phase method. It was found that solid solutions are formed in Bi2MgNb2-2xCo2xO9-δ series, foreign phases of MgNb2O6 and Bi5Nb3O15 are fixed in Bi2Mg1-xCoxNb2O9 samples, no impurity cobalt-containing phases were detected. The method of magnetic susceptibility and NEXAFS-spectroscopy investigated the electronic state and character of exchange interactions of cobalt atoms in solid solutions with the pyrochlore structure. According to X-ray spectroscopy and magnetic susceptibility of cobalt atoms in solid solutions in a dominant amount are in the charge state of Co(II) in the form of monomers and exchange-bound clusters mainly with antiferromagnetic type of exchange. Ceramics Co-doping of multicomponent bismuth niobate pyrochlore has at room temperature a high dielectric permeability of 84 and small dielectric losses of 0.001. The energy of activation of conductivity is equal to 0.75–1.03 eV. This type of ceramics with excellent dielectric properties can potentially be used as multilayer ceramic capacitors.

Stochastic optimal control formalism for an open quantum system

A stochastic procedure is developed which allows one to express Pontryagin's maximum principle for dissipative quantum system solely in terms of stochastic wave functions. Time-optimal controls can be efficiently computed without computing the density matrix. Specifically, the proper dynamical update rules are presented for the stochastic costate variables introduced by Pontryagin's maximum principle and restrictions on the form of the terminal cost function are discussed. The proposed procedure is confirmed by comparing the results to those obtained from optimal control on Lindbladian dynamics. Numerically, the proposed formalism becomes time and memory efficient for large systems, and it can be generalized to describe non-Markovian dynamics.

Non-metallic electronic regulation in CuCo oxy-/thio-spinel as advanced oxygen evolution electrocatalysts

Developing cost-effective and high-performance oxygen evolution reaction (OER) electrocatalysts has become the intense research on pursuing emerging renewable energy conversion, in which exploring and investigating the intrinsic nature of efficient and stable CuCo spinel catalysts toward OER in alkaline media is highly desirable. Herein, Cu1– x Co2+ x O4 oxy-spinel nanoflakes are fabricated by a facile hydrothermal method with the oxidation of ammonia water. In the same condition, Cu1– x -Co2+ x S4 thio-spinel nanospheres are formed without oxidation. In OER process, the as-obtained Cu1– x Co2+ x O4 nanoflakes and Cu1– x Co2+ x S4 nanospheres possess the anodic overpotential of 267 and 297 mV in alkaline media to drive the current density of 10 mA/cm2, respectively, outperforming the state-of-the-art noble metal catalyst of RuO2. X-ray photoelectron spectroscopy analysis exhibits the higher ratio value of Co(III)/Co(II) in Cu1– x Co2+ x O4 than that in Cu1– x Co2+ x S4, suggesting that the strongly-electronegative oxygen efficiently predominates in regulating valence states of Co active sites in spinel structures. Remarkably, density functional theory simulation further reveals that the increased valence state of Co could accelerate the electron exchange between catalysts and oxygen adsorbates during electrocatalysis, thus contributing to the higher OER activity of Cu1– x Co2+ x O4 catalysts. This work provides deep insight regarding the significance of non-metal element (O and S) in CuCo spinel structure catalysts, as well as presents a promising approach to exploit higher performance and grasp the mechanism of various non-noble-metal spinel catalysts for water oxidation.

Structural evolution of ZIF-67-derived catalysts for furfural hydrogenation

Zeolitic imidazolate framework-67 (ZIF-67) can be converted to metallic Co nanoparticles supported on N-doped carbon (Co/NC) through reduction. However, its unique properties, including extremely high surface area, isoreticular pore structure, and regular metal–organic network, disappear after high-temperature (>500 °C) reduction. Aggregated CoOx particles reduce the number of surface-active sites, resulting in poor catalytic activity. If the original ZIF-67 structure is maintained after the high-temperature reduction, promoting the uniform distribution of active sites in the porous carbon, the catalytic performance can be further improved. Herein, the correlation between the catalytic furfural hydrogenation performance, Co/NC morphology, and oxidation state of Co was investigated as a function of the H2 reduction temperature and time. The reduction of ZIF-67 at 400 °C for 6 h yields a highly dispersed Co/NC catalyst, while preserving the overall morphology. The resulting Co/NC-400-6 catalyst exhibits the highest activity, promoting high selectivity toward 2-methylfuran. The product selectivity can be further altered by incorporating Cu into ZIF-67 to produce furfuryl alcohol. With proper H2 treatment to minimize the damage to the intrinsic surface area and pore structure, metal–organic frameworks can be utilized as high-performance heterogeneous catalysts by maximizing the distribution of active sites.

Relation among Oxygen Stoichiometry, Structure, and Co Valence and Spin State in Single-Layer La2-xAxCoO4±δ (A = Ca, Sr) Perovskites.

We have investigated the role of oxygen stoichiometry and structural properties in the modulation of Co valence and spin state in single-layer La2-xAxCoO4±δ (A = Sr, Ca; 0 ≤ x ≤ 1) perovskites as well as the interplay between their local structural properties and the magnetic and charge-ordering phenomena. We show the results of high angular resolution powder X-ray diffraction and Co K-edge X-ray absorption and emission spectroscopy experiments on polycrystalline and single-crystal samples. The different doping-induced changes in the Co valence and spin state by Ca (or Sr) substitution can be understood in terms of the evolving oxygen stoichiometry. For Ca doping, the interstitial oxygen excess around the La/Ca atoms in underdoped samples is rapidly lost upon increasing the Ca content. The creation of oxygen vacancies leads to the stabilization of a mixed-valence Co2.5+ independently of the Ca content. In contrast, Sr substitution leads to almost stoichiometric samples and a lower oxygen vacancy concentration, which allows higher mixed-valence states for Co up to Co2.9+. The Co mixed-valence state along the two series is fluctuating between two valence states, Co2.4+ as in La2CoO4.2 and Co2.9+ as in LaSrCoO3.91, that become periodically ordered for the charge-ordered phases around the half-doping. The X-ray emission derived spin states agree well with the Co fluctuating mixed-valence state derived from X-ray absorption spectroscopy on consideration of a distribution of high-spin Co2+ and low-spin Co3+. Furthermore, there is no quenching of the orbital contribution for the high-spin Co2+, as concluded from a comparison with macroscopic magnetization measurements. Doping holes are mainly located in the ab plane and have a strong oxygen 2p character. The major lattice distortions, which are different for Sr and Ca doping, occur along the c axis, where changes in the oxygen stoichiometry take place. Moreover, charge-order transitions are clearly shown from the anomalous increase of the c lattice parameter with an increase in the temperature above 500 K but there is no signature for a temperature-dependent spin-state transition.

Equation of state for CO and CO2 fluids and their application on decarbonation reactions at high pressure and temperature

Ab initio molecular dynamics simulations were performed at pressures and temperatures up to 160 GPa and 4000 K, in order to obtain equations of state (EOS) for CO and CO2 fluids. We found that polymerisation of CO and CO2 fluids starts at low pressures, and that including the effect of polymerisation is essential for accurate EOS. EOSs for CO and CO2 determined from methods using experimental data, or classical potentials that ignore the changes in speciation, should be treated with caution when extrapolated beyond the examined pressures and temperatures. The obtained data was fitted to a modified Lee and Kesler EOS for both CO and CO2 fluids. The thermodynamic calculations for the decarbonation reactions of both MgCO3 and CaCO3 using the derived CO2 EOS reproduced the experimental data and theoretical calculations at low pressures. Both MgCO3 and CaCO3 pure phases are found to be stable in the upper mantle compared to CO2. However, they both become destabilised when approaching lower mantle conditions.

Understanding the relationship between the local crystal structure and the ferrimagnetic ordering of CoxMn3-xO4 (x = 0–0.5) solid solutions

The local crystal structure alterations in the tetrahedral positions of the hausmannite Mn3O4 structure by Co2+ ions and its consequence on the magnetic ordering are studied in detail. The cation composition, bond distance and bond angle of the CoxMn3-xO4 series (x = 0.0. 0.1, 0.3 and 0.5) is determined by XRD Rietveld refinement. The charge state of the elements Co, Mn and O are investigated using XPS measurements, which confirm the bivalent cobalt ion occupation in the tetrahedral lattice. Considerable reduction in tetrahedral and axial octahedral bonds with the introduction of Co2+ ions dramatically increased the Curie temperature (TC) from 43 K (Mn3O4) to 62 K (Co0.5Mn2.5O4). The Lotgering-Srinivasan-Seehra model is employed to study the canted spin arrangement and the exchange interactions of Co0.5Mn2.5O4. The presence of cluster glass transition at TP = 42 K in Co0.3Mn2.7O4 is well-established through the AC susceptibility measurements and it is further substantiated by Vogel-Fulcher law and dynamic scaling power law. The origin of the cluster glass state is confirmed by the calculated strong geometric frustration factor (f = 19.5), due to the inhomogeneous distribution of cobalt ions in the intermediate concentrations. Field cooled isothermal magnetic measurements corroborated the exchange bias phenomenon in the Co0.3Mn2.7O4 sample, because of the interaction between ferrimagnetic-cluster glass phases occurring below the spin freezing temperature TP.

In-situ growth of Co3O4 nanoparticles based on electrospray for an acetone gas sensor

In this study, Co3O4 nanoparticles were prepared using the electrospray method and were then deposited in-situ on a substrate to fabricate an acetone gas sensor. The physicochemical properties of the samples were investigated using scanning electron spectroscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The growth of the Co3O4 nanoparticles was confirmed by SEM. The Co3O4 nanoparticles showed the spinel structure, as revealed by the XRD results. The chemical composition of the prepared material and the chemical states of Co and O were investigated using XPS. The gas sensing properties of the electrosprayed Co3O4 nanoparticles were analyzed. The nanomaterials exhibited excellent acetone sensitivity. At the optimum working temperature of 200 °C, the response to 100 ppm acetone was 8.61, and the response and recovery times were 43 and 92 s, respectively. Moreover, sub-ppm acetone could be detected by the sensor. The Co3O4 nanoparticle-based sensor showed excellent sensitivity to acetone in the presence of methanol, ethanol, isopropanol, benzene, and ethyl acetate. The sensor showed a relative standard deviation of response of approximately 3.893%–100 ppm acetone over 10 days in the atmospheric environment. The acetone-sensing mechanism of the electrosprayed Co3O4 film was also investigated.

A posteriori error control for distributed elliptic optimal control problems with control constraints discretized by [formula omitted]-finite elements

A distributed elliptic control problem with control constraints is considered, which is formulated as a three field problem and consists of two variational equations for the state and the co-state variables as well as of a variational inequality for the control variable. Two discretization approaches with hp-finite elements are discussed: In the first discretization approach all variables (state, co-state and control) are discretized. A semi smooth Newton method is introduced for solving the resulting algebraic system. In the second discretization approach only the state and the co-state variables are discretized, whereas the control is determined by projection. A simple fixed point scheme is presented for the iterative solution of this approach. The main focus of the paper is on the derivation of reliable and efficient a posteriori error estimates, which enables hp-adaptive mesh refinements. In particular, the estimates can be applied to the iteration solutions, so that they can be used as a stopping criterion of the iterative solution schemes. In several numerical experiments the order of convergence of the (adaptive) discretization approaches and the efficiency as well as the reliability of the a posteriori error estimates are studied.

Regulating Photocatalysis by Spin-State Manipulation of Cobalt in Covalent Organic Frameworks.

While catalysis is highly dependent on the electronic structure of the catalyst, the understanding of catalytic performance affected by electron spin regulation remains challenging and rare. Herein, we have developed a facile strategy to the manipulation of the cobalt spin state over covalent organic frameworks (COFs), COF-367-Co, by simply changing the oxidation state of Co centered in the porphyrin. Density functional theory (DFT) calculations together with experimental results confirm that CoII and CoIII are embedded in COF-367 with S = 1/2 and 0 spin ground states, respectively. Remarkably, photocatalytic CO2 reduction results indicate that COF-367-CoIII exhibits favorable activity and significantly enhanced selectivity to HCOOH, accordingly much reduced activity and selectivity to CO and CH4, in sharp contrast to COF-367-CoII. The results highlight that the spin-state transition of cobalt greatly regulates photocatalytic performance. Theoretical calculations further disclose that the presence of CoIII in COF-367-Co is preferable to the formation of HCOOH but detrimental to its further conversion, which clearly accounts for its distinctly different photocatalysis over COF-367-CoII. To the best of our knowledge, this is the first report on regulating photocatalysis by spin state manipulation in COFs.