Molecular Water Oxidation Catalysts Research Articles

Efficient electrochemical water oxidation catalyzed by a novel nickel complex: Critical effect of the flexibility of pyridine-amine based pentadentate ligand on catalytic property

Efficient electrochemical water oxidation can be realized by reasonable modulation of the ligand structure of metal complex-based molecular water oxidation catalysts (WOCs). Herein, the synthesis and prowess in electrocatalytic water oxidation of a mononuclear water-soluble nickel complex, [Ni(tmbptu)(OH2)](ClO4)2 (1, tmbptu = 2,6,10-trimethyl-1,11-bis(2-pyridyl)-2,6,10-triazaundecanone), is reported for the first time. Complex 1 is found to be an efficient homogeneous WOCs under near neutral condition with long-term catalytic stability by a series of characterizations, including dynamic light scattering (DLS) measurement, scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray (EDX) analysis, chelation experiment, and Fe3+ test. Electrochemical tests reveal that water oxidation is accomplished via the generation of NiIV species generated by two successive e−/H+ proton coupled electron transfer (PCET) processes. Astonishingly, compared to the homologous complex [Ni(tmbptn)(OH2)](ClO4)2 (2, tmbptn = 2,5,8-trimethyl-1,9-bis(2-pyridyl)-2,5,8-triazanonane), which is a well-defined molecular WOC with high catalytic onset overpotential, 1 displays lower onset overpotential and much higher catalytic activity. This work suggesting that though the tertiary amine coordination environment have gain effect on the redox potential of metal center due to its poor sigma-donor effect, resulting in high onset overpotential of metal complex for water oxidation, this negative impact of the pyridine-amine ligand on the catalytic properties of complex can be weaken by adjusting the flexibility of backbone of those ligands.

Exploring Mechanistic Details and Catalyst Resilience in Electrocatalytic Water Oxidation with a Cu(II) Complex bearing a Redox‐Active ligand

Herein, we report that a copper complex [Cu(dpaq)](ClO4) (1) (H‐dpaq = 2‐[bis(pyridin‐2‐ylmethyl)]amino‐N‐quinolin‐8‐yl‐acetamide), acts as a molecular water oxidation catalyst (WOC) under strong basic condition. Complex 1 oxidizes water to dioxygen in 0.1 M phosphate buffer solution at pH 12.0, exhibiting a turnover frequency of 3.1 x 102 s‐1 at a low overpotential (η) of ~550 mV versus NHE at 1 mAcm‐2. A turnover number of 4.0 can be obtained during controlled potential electrolysis (CPE) using 0.25 mM complex 1 at a potential of 1.5 V at pH 12.0 for 3h. Post‐electrolysis analysis, rinse tests, and chelating assays collectively support the homogeneous nature of the electrocatalyst. Mechanistic investigations and quantum chemical calculations reveal a pathway wherein two successive ligand‐centered oxidations transform the catalyst into a Cu(II)(dpaq•)O•. intermediate. Absence of any metal centred oxidation renders the oxidized intermediate less electrophilic, resulting in the survival of the methylene groups present on the ligand backbone against oxidation. The formation of the O–O bond is proposed to proceed via two consecutive single electron transfers (SET) from incoming hydroxide ions to the formal CuIV‐oxo species.

Role of Active Centers in Predicting the Catalyst Turnover: A Theoretical Study.

Water oxidation catalysis has garnered significant attention due to its potential for sustainable energy conversion. Among molecular catalysts, [Fe(OTf)2 (Me2Pytacn)] complexes have exhibited notable turning-over rates. Although various [M(OTf)2 (Me2Pytacn)] complexes (M = Mn, Co, Ni) have been synthesized, however, the role of active centres has not been thoroughly investigated. In this study, we apply our newly developed catalytic models, efficiency conceptualization model (ECM) and the maximum kinetic efficiency MaxKinEff framework to assess the role of the active centres in its catalytic performance. Our computational analysis identifies cobalt-based [Co(OTf)2 (Me2Pytacn)] as a superior alternative for water oxidation reactions. Notably, cobalt catalysts exhibit a longer lifespan (~ 44 days) and higher turnover numbers (TON), with computed values of (ECM) = 3.30 h-1, (ECM) = 3456, (MaxKinEff) = 12.43 h-1, and (MaxKinEff) = 3616. These findings suggest that cobalt could play a pivotal role in improving the efficiency of molecular catalysts for water oxidation.

{Co4O4} Cubanes in a conducting polymer matrix as bio-inspired molecular oxygen evolution catalysts

Exploration of efficient molecular water oxidation catalysts for long-term application remains a key challenge for the conversion of renewable energy sources into fuels. Cuboidal {Co4O4} complexes keep attracting interest as molecular water oxidation catalysts as they combine features of both heterogeneous and homogeneous catalysis with bio-inspired motifs. However, the application of many cluster-based catalysts for the oxygen evolution reaction still requires new stabilization strategies. Drawing inspiration from the stabilizing effects of natural polymers, we introduce a conductive polymer-hybrid approach to covalently immobilize {Co4O4} cubane oxo clusters as oxygen evolution catalysts. Polypyrrole is applied as an efficient p-type conducting polymer that promotes hole transfer during the oxygen evolution reaction, resulting in higher turnover frequency compared to the pristine {Co4O4} oxo cluster and heterogeneous Co-oxide benchmarks. The asymmetric coordination of {Co4O4} not only mitigates catalyst decomposition pathways, but also increases the catalytic efficiency by exposing a directed cofacial dihydroxide motif during catalysis.

Synthesis, characterization and application of quinoxaline-based organic dyes as anodic sensitizers in photoelectrochemical cells

Three new D-A-π-A organic dyes (1a-c) containing a 2,3-diphenylquinoxaline core as the main chromophore were designed to act as sensitizers for the TiO2-based photoanode of dye-sensitized photoelectrochemical cells (DS-PEC) for water splitting. The dyes structures featured a cyanoacrylic acid group as the terminal acceptor/anchoring moiety and three different donor groups of moderate strength, namely mono- and dialkoxy-substituted benzenes, which were introduced to modulate the energies of the respective HOMO levels and enable the electron transfer from a Ru-based molecular water oxidation catalyst (WOC). Dyes 1a-c were synthesized following a C–H activation strategy and fully characterized. In addition, the previously known catalyst Ru(bda)(PyP)2 (bda = 2,2′-bipyridine-6,6′-dicarboxylate; PyP = pyridin-4-methyl phosphonic acid) was also prepared by modification of a reported procedure. The dynamics of charge transfer processes involving the dyes adsorbed on nanocrystalline TiO2 films were investigated by means of transient absorption spectroscopy. Photo-electrochemical experiments carried out on photoanodes functionalized with 1a-c and Ru(bda)(PyP)2 in 0.1 M aq. Na2SO4 electrolyte showed the production of photocurrents up to ca. 0.15 mA cm−2 at + 0.5 V vs. NHE, and highlighted how modifications of the TiO2 staining procedure can lead to significant differences in cell performances.

Role of Intragap States in Sensitized Sb-Doped Tin Oxide Photoanodes for Solar Fuels Production.

In view of developing photoelectrosynthetic cells which are able to store solar energy in chemical bonds, water splitting is usually the reaction of choice when targeting hydrogen production. However, alternative approaches can be considered, aimed at substituting the anodic reaction of water oxidation with more commercially capitalizable oxidations. Among them, the production of bromine from bromide ions was investigated long back in the 1980s by Texas Instruments. Herein we present optimized perylene-diimide (PDI)-sensitized antimony-doped tin oxide (ATO) photoanodes enabling the photoinduced HBr splitting with >4 mA/cm2 photocurrent densities under 0.1 W/cm2 AM1.5G illumination and 91 ± 3% faradaic efficiencies for bromine production. These remarkable results, among the best currently reported for the photoelectrochemical Br- oxidation by dye sensitized photoanodes, are strongly related to the occupancy extent of ATO's intragap (IG) states, generated upon Sb-doping, as demonstrated by comparing their performances with PDI-sensitized analogues on both undoped SnO2- and TiO2-passivated ATO scaffolds by means of (spectro)electrochemistry and electrochemical impedance spectroscopy. The architecture of the ATO-PDI photoanodic assembly was further modified via the introduction of a molecular iridium-based water oxidation catalyst, thus proving the versatility of the proposed hybrid interfaces as photoanodic platforms for photoinduced oxidations in PEC devices.

Rational Design of Improved Ru Containing Fe-Based Metal-Organic Framework (MOF) Photoanode for Artificial Photosynthesis.

Metal-Organic Frameworks (MOFs) recently emerged as a new platform for the realization of integrated devices for artificial photosynthesis. However, there remain few demonstrations of rational tuning of such devices for improved performance. Here, a fast molecular water oxidation catalyst working via water nucleophilic attack is integrated into the MOF MIL-142, wherein Fe3O nodes absorb visible light, leading to charge separation. Materials are characterized by a range of structural and spectroscopic techniques. New, [Ru(tpy)(Qc)(H2O)]+ (tpy = 2,2':6',2″-terpyridine and Qc = 8-quinolinecarboxylate)-doped Fe MIL-142 achieved a high photocurrent (1.6 × 10-3 A·cm-2) in photo-electrocatalytic water splitting at pH = 1. Unassisted photocatalytic H2 evolution is also reported with Pt as the co-catalyst (4.8 µmol g-1 min-1). The high activity of this new system enables hydrogen gas capture from an easy-to-manufacture, scaled-up prototype utilizing MOF deposited on FTO glass as a photoanode. These findings provide insights for the development of MOF-based light-driven water-splitting assemblies utilizing a minimal amount of precious metals and Fe-based photosensitizers.

Removing the Barrier in O-O Bond Formation Via the Combination of Intramolecular Radical Coupling and the Oxide Relay Mechanism.

The Ru(tda) catalyst has been a major milestone in the development of molecular water oxidation catalysts due to its outstanding performance at neutral pH. The role of the noncoordinating carboxylate group is to act as a nucleophile, donating an oxygen atom to the oxo group, thereby acting as an oxide relay (OR) mechanism for O-O bond formation. A substitution of the carboxylates for phosphonate groups has been proposed, resulting in the Ru(tPaO) catalyst, which has shown even more efficient performance in experimental characterization. In this study, we explore the feasibility of the OR mechanism in the newly reported Ru(tPaO) molecular catalyst. We investigated the catalytic cycle using density functional theory and identified a variation of the OR mechanism that involves radical oxygen atoms in O-O bond formation. We have also determined that the subsequent hydroxide nucleophilic attack is the sole rate-limiting step in the catalytic cycle. All activation free energies are very low, with a free-energy barrier of 2.1 kcal/mol for O-O bond formation and 4.2 kcal/mol for OH- nucleophilic attack.

Crystal structure of a water oxidation catalyst solvate with composition (NH4)2[FeIV(L-6H)]·3CH3COOH (L = clathrochelate ligand).

The synthetic availability of mol-ecular water oxidation catalysts containing high-valent ions of 3d metals in the active site is a prerequisite to enabling photo- and electrochemical water splitting on a large scale. Herein, the synthesis and crystal structure of di-ammonium {μ-1,3,4,7,8,10,12,13,16,17,19,22-dodeca-aza-tetra-cyclo-[8.8.4.13,17.18,12]tetra-cosane-5,6,14,15,20,21-hexa-onato}ferrate(IV) acetic acid tris-olvate, (NH4)2[FeIV(C12H12N12O6)]·3CH3COOH or (NH4)2[FeIV(L-6H)]·3CH3COOH is reported. The FeIV ion is encapsulated by the macropolycyclic ligand, which can be described as a dodeca-aza-quadricyclic cage with two capping tri-aza-cyclo-hexane fragments making three five- and six six-membered alternating chelate rings with the central FeIV ion. The local coord-ination environment of FeIV is formed by six deprotonated hydrazide nitro-gen atoms, which stabilize the unusual oxidation state. The FeIV ion lies on a twofold rotation axis (multiplicity 4, Wyckoff letter e) of the space group C2/c. Its coordination geometry is inter-mediate between a trigonal prism (distortion angle φ = 0°) and an anti-prism (φ = 60°) with φ = 31.1°. The Fe-N bond lengths lie in the range 1.9376 (13)-1.9617 (13) Å, as expected for tetra-valent iron. Structure analysis revealed that three acetic acid mol-ecules additionally co-crystallize per one iron(IV) complex, and one of them is positionally disordered over four positions. In the crystal structure, the ammonium cations, complex dianions and acetic acid mol-ecules are inter-connected by an intricate system of hydrogen bonds, mainly via the oxamide oxygen atoms acting as acceptors.

Efficient electrochemical water oxidation catalyzed by N4-coordinated nickel complexes under neutral conditions

Two novel nickel complexes are reported for the first time. Both complexes can catalyze water oxidation under neutral conditions with low onset overpotential. Combined experiments confirm that they are genuine molecular water oxidation catalysts.

Influence of substituents on the water oxidation performance for copper–bipyridine catalysts

Since it was first reported in 2012, copper-based molecular catalysts for water oxidation have gained significant attention. While investigations have endeavored to elucidate additional copper molecular catalysts for water oxidation and enhance their catalytic activities, few have systematically explored substituents' impact on their water oxidation performance. In this work, a series of copper-bipyridine catalysts, (2,2′-bipyridine)Cu(OH)2 derivatives with various substituents were synthesized by simply mixing the copper salts with 4,4′-R-2,2′-bipyridine ligands, where R represents seven distinct substituents. The UV–vis and FTIR spectra confirm the successful synthesis of the catalysts. However, only four of them are stable under the experimental conditions. The electrochemical studies show that their water oxidation potential follows the order of Cu-H < Cu-CH3 < Cu–OCH3 < Cu-CH2OH, indicating their water oxidation ability. Computation calculation indicates a linear relationship between the turnover frequency and the HOMO-LUMO energy gap. This work uncovers the influence of substituents on the catalytic properties of copper-bipyridine catalysts, offering valuable insights into the rational design of copper-based catalysts.

Catalytic Water Oxidation by Ruthenium Complexes with Pyridine Alkoxide Ligands

AbstractLigand design is crucial for the design of robust and efficient molecular water oxidation catalysts (WOCs) based on metal complexes. Herein we report the water oxidation studies of a series of Ru WOCs bearing bipyridine dialkoxide ligands with different substituents. Combined with density functional theory (DFT) calculations, the proposed water oxidation mechanism is bimolecular coupling (I2M) of two seven‐coordinate (CN7) Ru=O species. The use of bulky phenyl groups on the planar alkoxide ligand helps to stabilize the high oxidation CN7 intermediates, without loss of ligand flexibility. This strategy may be useful for the design of other active WOCs.

Pentanuclear iron complex for water oxidation: Spectroscopic analysis of reactive intermediates in solution and catalyst immobilization into the MOF-based photoanode

Photoelectrochemical water splitting can produce green hydrogen for industrial use and CO2-neutral transportation, ensuring the transition from fossil fuels to green, renewable energy sources. The iron-based electrocatalyst [FeII4FeIII(μ-3-O)(μ-L)6]3+ (LH = 3,5-bis(2-pyridyl)pyrazole) (1), discovered in 2016, is one of the fastest molecular water oxidation catalysts (WOC) based on earth-abundant elements. However, its water oxidation reaction (WOR) mechanism has not been yet fully elucidated. Here, we present in situ X-ray spectroscopy and electron paramagnetic resonance (EPR) analysis of electrochemical WOR promoted by (1) in water-acetonitrile solution. We observed transient reactive intermediates during the in situ electrochemical WOR, consistent with a coordination sphere expansion prior to the onset of catalytic current. At a pre-catalytic (∼+1.1 V vs. Ag/AgCl) potential, the distinct g ∼ 2.0 EPR signal assigned to FeIII/FeIV interaction was observed. Prolonged bulk electrolysis at catalytic (∼+1.6 V vs. Ag/AgCl) potential leads to the further oxidation of Fe centers in (1). At the steady state achieved with such electrolysis, the formation of hypervalent FeVO and FeIVO catalytic intermediates was inferred with XANES and EXAFS fitting, detecting a short FeO bond at ∼ 1.6 Å. (1) was embedded into MIL-126 MOF with the formation of a (1)-MIL-126 composite. The latter was tested in photoelectrochemical WOR and demonstrated an increase in electrocatalytic current upon visible light irradiation in acidic (pH = 2) water solution. The presented spectroscopic analysis gives further insight into the catalytic pathways of multinuclear systems and should help the subsequent development of more energy- and cost-effective water-splitting catalysts based on earth-abundant metals. Photoelectrocatalytic activity of (1)-MIL-126 confirms the possibility of creating an assembly of (1) inside a solid support and harnessing solar irradiation towards industrial applications of the catalyst.

Dangling Ligand Enables an Iron Hexa-Coordinated Molecular Catalyst for Water Oxidation by Photocatalysis

Dangling Ligand Enables an Iron Hexa-Coordinated Molecular Catalyst for Water Oxidation by Photocatalysis

(Invited) Water Oxidation Catalysis with Atomically Defined Active Sites on Nanostructured Materials for Solar Energy Applications

Devising cost effective methods for efficiently capturing and storing solar energy is among the grand challenges of science (1). We are using insights from studies of natural photosynthetic systems (2) to develop bioinspired materials for photo-electrochemical water oxidation and solar fuel production by using molecular catalysts and dyes attached to mesoporous metal oxide photoanodes. Molecular catalysts are known for their high activity and tunability, but their solubility and limited stability often restrict their use in practical applications. We are developing anchoring chemistry to attach molecular water-oxidation catalysts to metal oxide surfaces (3), which not only greatly increases the stability of the molecular catalyst but also improves the catalytic performance of the oxide material. Our progress on the development and characterization of molecular iridium, copper and manganese water-oxidation catalysts (4-5), along with their application for photoelectrochemical water oxidation (6) and solar fuel production, will be discussed. Directing Matter and Energy: Five Challenges for Science and the Imagination, U.S. Department of Energy, Washington, DC, December 2007.D.J. Vinyard and G.W. Brudvig, Annu. Rev. Phys. Chem. (2017) 68, 101.J.L. Troiano, R.H. Crabtree and G.W. Brudvig, ACS Appl. Mater. Interfaces (2022) 14, 6582.S.W. Sheehan et al., Nature Comm. (2015) 6, 6469.K.J. Fisher et al., ACS Catalysis (2017) 7, 3384.Y. Zhao et al., Proc. Natl. Acad. Sci. U.S.A. (2018) 115, 2902.

Bioinspired Active Site with a Coordination-Adaptive Organosulfonate Ligand for Catalytic Water Oxidation at Neutral pH

Many enzymes use adaptive frameworks to preorganize substrates, accommodate various structural and electronic demands of intermediates, and accelerate related catalysis. Inspired by biological systems, a Ru-based molecular water oxidation catalyst containing a configurationally labile ligand [2,2':6',2″-terpyridine]-6,6″-disulfonate was designed to mimic enzymatic framework, in which the sulfonate coordination is highly flexible and functions as both an electron donor to stabilize high-valent Ru and a proton acceptor to accelerate water dissociation, thus boosting the catalytic water oxidation performance thermodynamically and kinetically. The combination of single-crystal X-ray analysis, various temperature NMR, electrochemical techniques, and DFT calculations was utilized to investigate the fundamental role of the self-adaptive ligand, demonstrating that the on-demand configurational changes give rise to fast catalytic kinetics with a turnover frequency (TOF) over 2000 s-1, which is compared to oxygen-evolving complex (OEC) in natural photosynthesis.

Operando Condition Reaction Modeling Shows Highly Dynamic Attachment of Oligomeric Ruthenium Catalysts

To increase the stability and current density of molecular-catalyst-based electroanodes for water oxidation, immobilization of the catalysts at the electrode surface is a common strategy. A prominent example is the oligomerized Ru(tda) molecular catalyst, which showed outstanding current densities even at neutral pH values. One of the most challenging aspects of immobilized catalysts is to understand the interaction between the catalyst and the surface under operando conditions. Experiments are often performed under model conditions, and computational methods to study reaction steps are typically limited to a few hundred atoms. In this study, we combined three computational methods, density functional theory electronic structure computations, molecular dynamics for large-scale simulations of the catalyst–solid interaction, and empirical valence bond for reaction modeling the catalyst at the interface of a large carbon support and a phosphate water buffer. These techniques allowed us to explore the combined effects of solvent, hydrophobic directionality, and electric field on the attachment and reactivity of a Ru(tda) pentamer at a graphene surface. Our simulations have a perfect agreement with the experimental characterization under model conditions. However, we find that under operando conditions, where the catalyst is oxidized to the active RuV state, with a phosphate-containing electrolyte and an applied electric field, the attachment is completely reversed compared to the model conditions with RuII and organic solvents. This reversed attachment leads to a water-excluded region close to the active RuV═O center. The EVB reaction modeling showed that the reaction could still proceed to form an O–O bond via an oxide relay mechanism, where a dangling carboxylate reacts with the oxo via nucleophilic attack. We find that the activation energies are identical in water solution and at the electrode surface, showing how this mechanism is key to highly active molecular water oxidation catalysts immobilized on surfaces. Since attachment to surfaces could have a strong, and often negative, influence on the reactions, this study provides a guideline on how to model reactions without compromising the complexity of the electrode environment.

Metamorphic oxygen-evolving molecular Ru and Ir catalysts.

Today sustainable and clean energy conversion strategies are based on sunlight and the use of water as a source of protons and electrons, in a similar manner as it happens in Photosystem II. To achieve this, the charge separation state induced by light has to be capable of oxidising water by 4 protons and 4 electrons and generating molecular oxygen. This oxidation occurs by the intermediacy of a catalyst capable of finding low-energy pathways via proton-coupled electron transfer steps. The high energy involved in the thermodynamics of water oxidation reaction, coupled with its mechanistic complexity, is responsible for the difficulty of discovering efficient and oxidatively robust molecules capable of achieving such a challenging task. A significant number of Ru coordination complexes have been identified as water oxidation catalysts (WOCs) and are among the best understood from a mechanistic perspective. In this review, we describe the catalytic performance of these complexes and focus our attention on the factors that influence their performance during catalysis, especially in cases where a detailed mechanistic investigation has been carried out. The collective information extracted from all the catalysts studied allows one to identify the key features that govern the complex chemistry associated with the catalytic water oxidation reaction. This includes the stability of trans-O-Ru-O groups, the change in coordination number from CN6 to CN7 at Ru high oxidation states, the ligand flexibility, the capacity to undergo intramolecular proton transfer, the bond strain, the axial ligand substitution, and supramolecular effects. Overall, combining all this information generates a coherent view of this complex chemistry.

Efficient electrochemical water oxidation mediated by different substituted manganese-salophen complexes

• The electrocatalytic role of different substituted Mn II salophen complexes was investigated for water oxidation. • It was revealed that the studied complexes show excellent activity for OER. • The overpotential for the OER was in the range of 345–420 mV. • It was speculated that the O O bond formation occurs by oxidizing the active center of Mn complexes. • The Mn II complexes catalyzed the OER as real electrocatalysts. Developing robust and efficient water oxidation catalysts is an essential challenge in water splitting. In this work, the electrocatalytic behavior of the modified carbon paste electrodes with different substituted Mn II salophen complexes, MnL 1 -MnL 3 , (H 2 L 1 = N,N′-bis(salicylidene)-1,2-diaminobenzene, H 2 L 2 = N,N′-bis(salicylidene)-4-bromo-1,2-diaminobenzene and H 2 L 3 = N,N′-bis(2-hydroxy-3-methoxybenzilidine)-1,2-diaminobenzene) was evaluated for water oxidation by electrochemical methods. All three complexes were found highly effective, stable, and robust catalysts for water oxidation. Electrochemical experiments, Field emission-scanning electron microscope (SEM), energy-dispersive X-ray (EDX), and powder X-ray diffraction (PXRD) analyses indicated that the studied Mn II salophen complexes are molecular catalysts for water oxidation in origin. Cyclic voltammetry experiments in different pHs displayed that the O O bond formation probably occurs by oxidizing the active center of Mn II complexes through proton-coupled electron transfer (PCET). The results showed that the nature of the substituent on the salophen ligand could not affect the stability of the complexes under applied electrochemical conditions. It was found that Mn oxide nanostructures obtained by the thermal decomposition of MnL 1 can also effectively catalyze the reaction, but in comparison with MnL 1 , they have lower activity.

BiVO4 photoanode modification by synergic dual-conjugated organic materials

Organic conjugated materials have presented considerable application potential in the field of photoelectrochemical (PEC) water splitting. In this study, two organic conjugated materials, two dimension carbon nitride (2D-C 3 N 4 ) and organic cobalt molecular catalyst ((H 3 O) 6 ·[Co 4 (H 2 O) 4 (HPMIDA) 2 (PMIDA) 2 )]·2H 2 O) (OCM), are fabricated in turn on the surface of bismuth vanadate (BVO) photoanode. Basing on the synergistic effect of 2D-C 3 N 4 and OCM, the PEC property of the modified BVO photoanode increases three times higher than that of bare BVO photoanode at 1.23 V vs. RHE by increasing reaction active surface, promoting charge separation, and reducing reaction overpotential. This study shows that organic conjugated materials can not only form an effective heterojunction system with semiconductor materials and improve surface catalytic activity, but also assemble easily by the strong affinity between g-C 3 N 4 and OCM. Therefore, it provides a novel and efficient modification method by dual-conjugated organic materials to improve the PEC performance of photoelectrodes. • Development of 2D-C 3 N 4 /organic cobalt molecular dual-conjugated water oxidation catalyst. • 2D-C 3 N 4 /organic cobalt molecular catalyst modified BiVO 4 photoanode was prepared by first time. • A synergistic effect was found between conjugated 2D-C 3 N 4 and organic cobalt molecular. • A photocurrent density of BiVO 4 photoanode increased three times after dual-conjugated molecular modification.