Water Splitting Cells Research Articles

N/P Co‐doped Micro‐/Mesoporous Carbons Derived from Polyvinyl Pyrrolidone–Zn0.2@ZIF‐67 with Tunable Metal Valence States towards Efficient Water Splitting

AbstractThe enhancement of electrocatalytic water splitting by modulating the intrinsic electronic environment of active sites has recently attracted lots of interest. Herein, cobalt‐cobalt oxide (CoOx) at carbons derived from metal‐organic frameworks (Zn0.2@ZIF‐67) have been modulated by using post‐phosphine (P‐CoOx/NCs), acid leaching (Co/NCs), and oxidation (O−CoOx/NCs) treatments. With the assistance of polyvinyl pyrrolidone, the resultant carbons obtain a high surface area (645.7 m2 g−1) as well as a micro‐/mesoporous system after carbonization at 920 °C. These advantages not only enhance the catalytic performance of catalysts, but also facilitate the charge transfer between interfaces towards the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). As a result, the constructed water splitting cell fabricated with 900P‐CoOx/NCs requires a low overpotential (89 mV and 343 mV vs. reservable hydrogen electrode respectively) to drive HER and OER at 10 mA cm−2, a low cell voltage (1.69 V), and a high stability with only 4.9 % decay after 15 hours operation in the alkaline medium.

Superhydrophilicity boron-doped cobalt phosphide nanosheets decorated carbon nanotube arrays self-supported electrode for overall water splitting

Transition metal borides (TMBs) or phosphides (TMPs) have attracted great attention to the design of bifunctional electrocatalysts for energy storage. The superaerophobicity and superhydrophilicity of the catalytic electrode surface are crucial factors to determine the reaction process of the gas electrode. Herein, we report a self-supported electrode of carbon nanotube (CNTs) array grown on carbon cloth (CC) modulated together by boron-doped cobalt phosphide (CoP-B/CNTs/CC). The electrode requires the overpotential of 73.8 mV and 189.5 mV at the current density of ±10 mA cm−2 for hydrogen and oxygen evolution reactions in an alkaline electrolyte (1.0 M KOH), respectively, meanwhile maintaining outstanding long-term durability for more than 300 h. The excellent activity of CoP-B/CNTs/CC is attributed to boron doping regulating its electronic structure and further enriching active sites. The attractive stability of CoP-B/CNTs/CC is due to the unique geometric structure of the self-supported electrode. Furthermore, the superaerophobicity and superhydrophilicity of the electrode surface also accelerate the reaction process of the gas electrode. Expectedly, water splitting cells assembled using CoP-B/CNTs/CC electrodes as cathode and anode, respectively, require a cell voltage of 1.54 V at 10 mA cm−2, which is lower than that of the Pt/C/CC||RuO2/CC couple (1.69 V at 10 mA cm−2). Importantly, CoP-B/CNTs/CC||CoP-B/CNTs/CC achieve stable cell voltage under the step current changes (10 mA cm−2, 50 mA cm−2, and 100 mA cm−2) over 300 h. This work highlights a new path to understanding the effects of the static and dynamic behavior of bubbles on the surface of self-supporting electrodes on catalytic performance.

Enhanced electrocatalytic performance of CuxNi1-xS Nanoflakes for overall water splitting

For long-term energy storage and conversion, the design of commercial and high-performance catalysts for bifunctional electrocatalytic water splitting is critical. We report the efficient method to prepare CuxNi1-xS Nanoflakes (NFs) on binder-free and large area plastic chip electrodes. CuxNi1-xS NSs show superior overall water splitting with optimized Cu-amount. The synthesized catalysts perform well in 1.0 M KOH alkaline media for simultaneous hydrogen and oxygen evolution, with relatively low overpotential, efficient kinetics, and sustained electrolysis durability. Impressively, it is found that Cu-doping enhances the chemical and environmental stability, beneficial for the practical application. By modifying the electronic structure, Cu-atom doping promotes the easy flow of electrons, which leads to incredible rise in the electrocatalytic activity with over potential of 152 mV for HER and 189 mV for OER on CuxNi1-xS. Bi-functional water splitting cell generates 10 mA/cm2 current density at cell voltage of 1.74 V. Encouragingly, current density of 80 mA/cm2 can be generated at potential of 2.61 V with optimized chemical composition of CuxNi1-xS based electrodes. CuxNi1-xS demonstrates excellent stability for bi-functional water electrolysis at 20 mA/cm2 for more than 18 h. This research lays forth a viable technique for developing enhanced bi-functional electrocatalysts that can be used to substitute noble metals in a range of renewable energy applications.

Engineering High-Entropy Duel-Functional nanocatalysts with regulative oxygen vacancies for efficient overall water splitting

High-entropy materials (HEMs) have attracted growing attention in catalysis fields owing to their multielement synergy and tunable electronic configuration. As one of the commonest HEMs, high-entropy oxides (HEOs), however, are far from satisfactory in terms of their high crystallization with insufficient active sites. Herein, a surface activation strategy is proposed to engineer high-activity HEOs electrocatalysts in which ample surface oxygen vacancies (OVs) are imported by means of resin templating and temperature regulation. As a result, the modulated (Fe0.27Ni0.35Co0.24Cr0.10Mn0.04)2O3-δ HEO with stable structure as well as large electrochemical surface area (ECSA) exhibits robust electrocatalytic activity towards both oxygen evolution reaction (OER, η10 = 174 mV) and hydrogen evolution reaction (HER, η10 = 60 mV). Correspondingly, as-assembled water splitting cell only requires a low voltage of 1.55 V to achieve 10 mA cm−2 current density, far superior to that of 1.72 V using the commercial noble metal electrocatalysts. This work opens up a new avenue in designing structure-stable HEOs for efficient electrocatalytic applications.

Fast formation of thin TiOx layer on titanium surface enabling a broadband light capture and fast charge carrier transfer

Improving light absorption and conversion ability is essential to improving the performance of photoelectrochemical (PEC) cells in converting and storing solar radiation into chemical energy. As part of this, realizing broadband light absorption in the wavelength of 250–2500 nm is promising to improve solar energy utilization. Previous studies have typically relied on noble metal functional materials to realize visible light harvesting over broadband light capture in PEC water splitting (WS) cells. Here, we report an electrochemical oxidation method to prepare thin TiOx layer on a Ti-foil surface. A nanostructured film is formed within 10–60 s with a tunable absorption range between 250 and 2500 nm, going beyond the 420 nm absorption edge of TiO2. In addition to superior light capture ability, the film shows a 10-fold enhancement in the charge carrier transfer rate under AM 1.5 G light compared to that measured under dark conditions. The method proposed is simple, fast, and low-cost, and it has potential for large-area PEC cells with promoted charge carriers’ transfer.

Boron and Sodium Doping of Polymeric Carbon Nitride Photoanodes for Photoelectrochemical Water Splitting.

Polymeric carbon nitride is a promising photoanode material for water-splitting and organic transformation-based photochemical cells. Despite achieving significant progress in performance, these materials still exhibit low photoactivity compared to inorganic photoanodic materials because of a moderate visible light response, poor charge separation, and slow oxidation kinetics. Here, the synthesis of a sodium- and boron-doped carbon nitride layer with excellent activity as a photoanode in a water-splitting photoelectrochemical cell is reported. The new synthesis consists of the direct growth of carbon nitride (CN) monomers from a hot precursor solution, enabling control over the monomer-to-dopant ratio, thus determining the final CN properties. The introduction of Na and B as dopants results in a dense CN layer with a packed morphology, better charge separation thanks to the in situ formation of an electron density gradient, and an extended visible light response up to 550nm. The optimized photoanode exhibits state-of-the-art performance: photocurrent densities with and without a hole scavenger of about 1.5 and 0.9mA cm-2 at 1.23V versus reversible hydrogen electrode (RHE), and maximal external quantum efficiencies of 56% and 24%, respectively, alongside an onset potential of 0.3V.

MXenes and MXene-based composites for energy conversion and storage applications

MXenes have received extensive attention from scholars due to their unique layered structure, significant electrical conductivity, and excellent mechanical properties. In addition to their pristine forms, they could also be incorporated with other components for attaining hybrids and nanocomposites, accompanying with amplified functionalities. It has been widely used in lithium batteries, supercapacitors, electromagnetic shielding, tumor therapy, biosensors, photocatalysis, and other fields, and has shown great application potential in energy conversion and storage. The purpose of this article is to encyclopaedically overview the latest progress in synthesis and characterization of MXenes, while their potential applications in energy conversation such as water splitting and solar cells, as well as in energy storage such as Li-ion batteries, supercapacitors, and hydrogen energy will be comprehensively elaborated. Development opportunities and challenges are summarized.

A minireview on 3D printing for electrochemical water splitting electrodes and cells

The adoption of additive manufacturing (also known as 3D printing) for electrochemically related applications is receiving increased attention from the research community, particularly for water electrolysis driven by renewable energy. Additive manufacturing has demonstrated its great potential in the structural design of complex geometry and customization. Given the recent development of several fast-prototyping materials and methods, examining the gaps of electrocatalytic electrode materials and apparatus between the lab scale and industrial scale is important. In this paper, we have summarized the state-of-art 3D printing technologies and 3D printing techniques used in water electrolysis systems—both electrodes and reaction cells. The suitability and advantages of 3D printing methods in developing and designing water-splitting reaction systems are thoroughly discussed. In addition, recent progress demonstrating 3D-printed electrodes and water-splitting cells is reviewed. Finally, future directions for this developing field of research are given along with current difficulties.

Activation stainless steel with electrochemical etching-hydrothermal as an efficient and stable alkaline water oxidation electrode

Stainless steel (SS) has great potential to become an efficient oxygen evolution reaction (OER) catalytic material, but an effective activation method is still lacking. Here, an electrochemical etching-hydrothermal activation strategy is proposed to turn SS into an efficient and stable OER electrode, which can deliver high current density of 300 mA cm−2 with only 314 mV, as well as offers a low Tafel slope of 30 mV dec−1. The catalytic phase formed by the activation has a low surface Ni/Fe ratio and completely disobeys the traditional “Fe-effect” activity trend. The performed O–K edge X-ray adsorption spectra revealed that the high valence states of Ni sites with modified electronic structure may be responsible for the enhanced OER performance. More importantly, the assembled overall water-splitting cell showed that it can withstand long-term durability of 100 h at an ultra-high current density of 2 A cm−2. The strategy presented here could yield an opportunity to convert SS into an efficient and robust catalyst for alkaline water oxidation and is expected to lead to more promising ones due to the diverse composition of SS.

Ferromagnetic single-atom spin catalyst for boosting water splitting.

Heterogeneous single-atom spin catalysts combined with magnetic fields provide a powerful means for accelerating chemical reactions with enhanced metal utilization and reaction efficiency. However, designing these catalysts remains challenging due to the need for a high density of atomically dispersed active sites with a short-range quantum spin exchange interaction and long-range ferromagnetic ordering. Here, we devised a scalable hydrothermal approach involving an operando acidic environment for synthesizing various single-atom spin catalysts with widely tunable substitutional magnetic atoms (M1) in a MoS2 host. Among all the M1/MoS2 species, Ni1/MoS2 adopts a distorted tetragonal structure that prompts both ferromagnetic coupling to nearby S atoms as well as adjacent Ni1 sites, resulting in global room-temperature ferromagnetism. Such coupling benefits spin-selective charge transfer in oxygen evolution reactions to produce triplet O2. Furthermore, a mild magnetic field of ~0.5 T enhances the oxygen evolution reaction magnetocurrent by ~2,880% over Ni1/MoS2, leading to excellent activity and stability in both seawater and pure water splitting cells. As supported by operando characterizations and theoretical calculations, a great magnetic-field-enhanced oxygen evolution reaction performance over Ni1/MoS2 is attributed to a field-induced spin alignment and spin density optimization over S active sites arising from field-regulated S(p)-Ni(d) hybridization, which in turn optimizes the adsorption energies for radical intermediates to reduce overall reaction barriers.

CoMoO4-CoP/NC heterostructure anchored on hollow polyhedral N-doped carbon skeleton for efficient water splitting

We report the synthesis and electrocatalytic properties of a CoMoO4-CoP heterostructure anchored on a hollow polyhedral N-doped carbon skeleton (CoMoO4-CoP/NC) for water-splitting applications. The preparation involved the anion exchange of MoO42- to the organic ligand of ZIF-67, the self-hydrolysis of MoO42-, and NaH2PO2 phosphating annealing. CoMoO4 was found to enhance thermal stability and prevent active site agglomeration during annealing, while the hollow structure of CoMoO4-CoP/NC provided a large specific surface area and high porosity that facilitated mass transport and charge transfer. The interfacial electron transfer from Co to Mo and P sites promoted the generation of electron-deficient Co sites and electron-enriched P sites, which accelerated water dissociation. CoMoO4-CoP/NC exhibited excellent electrocatalytic activity for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in 1.0 M KOH solution, with overpotentials of 122 mV and 280 mV at 10 mA cm−2, respectively. The CoMoO4-CoP/NC‖CoMoO4-CoP/NC two-electrode system only required an overall water splitting (OWS) cell voltage of 1.62 V to achieve 10 mA cm−2 in an alkaline electrolytic cell. In addition, the material showed comparable activity to 20% Pt/C‖RuO2 in a pure water home-made membrane electrode device, demonstrating potential for practical applications in proton exchange membrane (PEM) electrolyzers. Our results suggest that CoMoO4-CoP/NC is a promising electrocatalyst for efficient and cost-effective water splitting.

In Situ Filling of the Oxygen Vacancies with Dual Heteroatoms in Co3O4 for Efficient Overall Water Splitting.

Electrocatalytic water splitting is a crucial area in sustainable energy development, and the development of highly efficient bifunctional catalysts that exhibit activity toward both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is of paramount importance. Co3O4 is a promising candidate catalyst, owing to the variable valence of Co, which can be exploited to enhance the bifunctional catalytic activity of HER and OER through rational adjustments of the electronic structure of Co atoms. In this study, we employed a plasma-etching strategy in combination with an in situ filling of heteroatoms to etch the surface of Co3O4, creating abundant oxygen vacancies, while simultaneously filling them with nitrogen and sulfur heteroatoms. The resulting N/S-VO-Co3O4 exhibited favorable bifunctional activity for alkaline electrocatalytic water splitting, with significantly enhanced HER and OER catalytic activity compared to pristine Co3O4. In an alkaline overall water-splitting simulated electrolytic cell, N/S-VO-Co3O4 || N/S-VO-Co3O4 showed excellent overall water splitting catalytic activity, comparable to noble metal benchmark catalysts Pt/C || IrO2, and demonstrated superior long-term catalytic stability. Additionally, the combination of in situ Raman spectroscopy with other ex situ characterizations provided further insight into the reasons behind the enhanced catalyst performance achieved through the in situ incorporation of N and S heteroatoms. This study presents a facile strategy for fabricating highly efficient cobalt-based spinel electrocatalysts incorporated with double heteroatoms for alkaline electrocatalytic monolithic water splitting.

Fully inkjet-printed large-scale photoelectrodes

Small-area photoelectrodes are used to study fundamental science and material development for photoelectrochemical (PEC) water splitting cells at the laboratory scale. For practical applications, however, one needs to develop scalable geometrical designs and architectures of large photoelectrodes as well as their fabrication using low-cost, solution-processed, scalable methods. In this perspective, we first discuss the device physics concepts for developing large photoelectrodes using dimensional engineering (size, geometry, shape, and structures) and scalable architectures (such as symmetric and asymmetric designs with gridlines as well as monolithically integrated modules with interconnections), similar to the earlier development of large thin-film photovoltaic cells. Finally, we propose a novel and strategic protocol to fabricate these designs for the development of large-photoelectrode modules via commercially deployable, fully inkjet-printing as a solution processed thin-film deposition method. Small-area photoelectrodes are used to study fundamental science and material development for photoelectrochemical (PEC) water splitting cells at the laboratory scale. For practical applications, however, one needs to develop scalable geometrical designs and architectures of large photoelectrodes as well as their fabrication using low-cost, solution-processed, scalable methods. In this perspective, we first discuss the device physics concepts for developing large photoelectrodes using dimensional engineering (size, geometry, shape, and structures) and scalable architectures (such as symmetric and asymmetric designs with gridlines as well as monolithically integrated modules with interconnections), similar to the earlier development of large thin-film photovoltaic cells. Finally, we propose a novel and strategic protocol to fabricate these designs for the development of large-photoelectrode modules via commercially deployable, fully inkjet-printing as a solution processed thin-film deposition method.

Multifunctional electrocatalyst based on MoCoFe LDH nanoarrays for the coupling of high efficiency Electro-Fenton and water splitting process

Novel MoCoFe layered double hydroxide (LDH) nanoarray catalysts were prepared by a one-step solvothermal method. These catalysts served as multifunctional catalysts for the coupling of overall water splitting with the Electro-Fenton process. MoCoFe LDH displayed different array structures evolving with Mo content, which results in different catalytic activities in the Oxygen Reduction Reaction (ORR), Oxygen Evolution Reaction (OER), and Hydrogen Evolution Reaction (HER) processes. Among them, Mo2CoFe LDH exhibited about 90% H2O2 selectivity over a wide voltage range and almost 100% degradation efficiency of sulfonamide antibiotics within 45 min. This was due to more open nanowire array structures and bond expansion resulting from the Mo introduction. Density Functional Theory (DFT) calculations showed that the addition of Mo atoms significantly reduced the energy barrier of H2O2 generation at the active site of Co. Meanwhile, Mo0.5CoFe LDH displayed competitive OER performance with an overpotential of 190 mV (vs. RHE) and HER activity with an overpotential of 78 mV@10 mA cm−2. The water splitting cell consisting of Mo0.5CoFe LDH electrodes only required a voltage of 1.53 V to achieve a current density of 10 mA cm−2. This was due to the generation of the crystal-amorphous interface structure via the substitution of Mo for the metal sites in LDH, which contributed to the internal active site exposure. The crystallization-amorphous structure promotes an increase in the number of active sites in terms of unit area by accelerating the M−OH to M−OOH reconfiguration, in addition to that, corrosion resistance and self-healing properties of this structure also helps to improve the stability and durability of the material during the OER process. Noteworthy, the Electro-Fenton/water-splitting coupling device was constructed, benefiting from the excellent Electro-Fenton and water electrolysis performance in alkaline solutions. The complete decolorization of 20 mg L-1 methyl blue could be achieved within 80 min at pH = 14 (Iwater-splitting = 37 mA cm−2, IEF = 8 mA cm−2), and Faraday efficiency of water splitting still remains above 95% after coupling EF. This novel coupling device may help to improve the energy utilization in the electrocatalytic process.

TiO2–SiO2 Self-Standing Materials bearing Hierarchical Porosity: MUB-200(x) Series toward 3D-Efficient VOC Photoabatement Properties

Three-dimensional photoactive self-standing porous materials have been synthesized through the integration of soft chemistry and colloids (emulsions, lyotrope mesophases, and P25 titania nanoparticles). Final multiscale porous ceramics bear 700-1000 m2 g-1 of micromesoporosity depending on the P25 nanoparticle contents. The applied thermal treatment does not affect the P25 anatase/rutile allotropic phase ratio. Photonic investigations correlated with the foams' morphologies suggest that the larger amount of TiO2 that is introduced, the larger the walls' density and the smaller the mean size of the void macroscopic diameters, with both effects inducing a reduction of the photon transport mean free path (lt) with the P25 content increase. A light penetration depth in the range of 6 mm is reached, thus depicting real 3D photonic scavenger behavior. The 3D photocatalytic properties of the MUB-200(x) series, studied in a dynamic "flow-through" configuration, show that the highest photoactivity (concentration of acetone ablated and concentration of CO2 formed) is obtained with the highest monolith height (volume) while providing an average of 75% mineralization. These experimental results validate the fact that these materials, bearing 3D photoactivity, are paving the path for air purification operating with self-standing porous monolith-type materials, which are much easier to handle than powders. As such, the photocatalytic systems can now be advantageously miniaturized, thereby offering indoor air treatment within vehicles/homes while drastically limiting the associated encumbrance. This volumetric counterintuitive acting mode for light-induced reactions may find other relevant advanced applications for photoinduced water splitting, solar fuel, and dye-sensitized solar cells while both optimizing photon scavenging and opening the path for the miniaturization of the processes where encumbrance or a foot-print penalty would be advantageously circumvented.

Analysis of XGaO3 (X = Ba and Cs) cubic based perovskite materials for photocatalytic water splitting applications: a DFT study

Energy conversion has become an important technology for meeting energy production and consumption in the modern era. Water splitting and solar cell technologies are projected to close the gap between demand and consumption. Therefore, XGaO3 (X = Ba and Cs) compounds having characteristics i.e., electrical, optical, mechanical, and structural are depicted by using a density functional theory (DFT) based CASTEP software with ultrasoft pseudo-potential plane-wave and Generalized Gradient Approximation and Perdew Burke Ernzerhof exchange correlation functional (GGA-PBE). According to the findings, all of these compounds have a cubic “pm3m” structure with space group 221. The CsGaO3 and BaGaO3 have direct and indirect band gaps, with respect to electronic band-structure recreations. Density of states like total density of states (TDOS) and partial density of states (PDOS) commend the extent of localization of electrons in numerous bands. The optical properties of these compounds are explored by adjusting dispersion curve/relation for theoretical dielectric function (DF) scale to the corresponding peaks. As a result, these materials could be used to consume light in the visible zone via photo catalysis. CsGaO3 in combination with BaGaO3 can produce effective results, so these compounds have a remarkable potential application for sensing and water splitting.

A Mini Review on Transition Metal Chalcogenides for Electrocatalytic Water Splitting: Bridging Material Design and Practical Application

Hydrogen is believed to be one of the essential clean secondary energy sources in the energy structure revolution of both industry and daily life. Driven by renewable electricity such as solar and wind power, water electrolysis for hydrogen production is deemed as one of the main processes of green hydrogen production in the future by both academia and industry. Transition metal chalcogenides (TMCs) are promising candidates to replace noble metals as earth-abundant electrocatalysts for water splitting. However, it remains challenging to further improve the electrocatalytic activity and long-term stability of TMCs, especially in a practical water electrolyzer. This Review summarizes the recent advances and the strategies of optimizing the electrocatalytic activities of TMCs toward water splitting as well as the latest investigations on the surface reconstructions of TMCs during water electrolysis. The performances of TMCs in practical electrocatalytic water splitting cells are particularly discussed. Finally, a concluding remark and perspective is provided, and we hope to inspire future works in this area, narrowing the gap between material design and practical application.

Dopant-Induced Surface Self-Etching of Cobalt Carbonate Hydroxide Boosts Efficient Water Splitting.

Herein, vanadium-doped cobalt carbonate hydroxide, V-CoCH, was synthesized as efficient catalyst for water splitting. Vanadium species were partially dissolved in the early stages of the oxygen-evolution reaction (OER), inducing self-etching of the catalyst surface, which is helpful for catalyst surface reconstruction and resulted in a higher number of active sites and oxygen vacancies. The synergy between V-doping and oxygen vacancies improved the catalytic activity: V-CoCH showed an exceptional OER catalytic performance with an overpotential of 183 mV at 10 mA cm-2 . The water-splitting cell consisting of V-CoCH only required 1.52 V to reach 10 mA cm-2 . Theoretical calculations revealed that vanadium in V-CoCH played an important role in electron regulation of active sites. The oxygen vacancies had an important effect on improvement of the OER performance through not only the exposure of more active sites but also through modulation of the electronic structure. This work provides an effective strategy for constructing high-performance electrocatalysts.

The Implications of Coupling an Electron Transfer Mediated Oxidation with a Proton Coupled Electron Transfer Reduction in Hybrid Water Electrolysis.

Electrolysis of water is a sustainable route to produce clean hydrogen. Full water-splitting requires a high applied potential, in part because of the pH-dependency of the H2 and O2 evolution reactions (HER and OER), which are proton-coupled electron transfer (PCET) reactions. Therefore, the minimum required potential will not change at different pHs. TEMPO [(2,2,6,6-tetramethyl-1-piperidin-1-yl)oxyl], a stable free-radical that undergoes fast electro-oxidation by a single-electron transfer (ET) process, is pH-independent. Here, we show that the combination of PCET and ET processes enables hydrogen production from water at low cell potentials below the theoretical value for full water-splitting by simple pH adjustment. As a case study, we combined the HER with the oxidation of benzylamine by anodically oxidized TEMPO. The pH-independent electrocatalytic oxidation of TEMPO permits the operation of a hybrid water-splitting cell that shows promise to perform at a low cell potential (≈1 V) and neutral pH conditions.

The coupling effect of carbon spheres and cobalt-involved carbon nitrides stacked on TiO2 nanorod arrays for promoted solar water oxidation

Photoanode materials typically exhibit good stability and environmentally and economically properties in solar water splitting cells, while they always suffer from the narrow light absorption range, heavy surface charge combination and sluggish surface reaction kinetics. Herein, we design an efficient and reproducible photoanode by stacking amorphous carbon spheres (CSs) and cobalt-involved carbon nitrides (Co-CNs) on surface of TiO2 nanorod arrays. CSs work as light sensitizer for broadening the light absorption range of photoanode and promoting the utilization of solar energy, which further improved by Co-CNs partially. In addition, CSs increase the conductivity of photoanode, as a transport channel for improving the charge migration. Co-CNs introduce many active sites on surface of photoanode for facilitated solar water oxidation. The best constructed TiO2/CSs/Co-CNs photoanode exhibits an impressive photocurrent density of ∼1.73 mA/cm2 (at 1.23 V vs RHE). The staking method of various functional materials provides one promising strategy for the modification of catalysts.