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Photocatalytic conversion of CO

Photocatalytic conversion of CO2 into chemical fuels is a promising approach to tackle carbon emission and global warming. Herein, we promote a cobalt dicyanamide coordination compound, Co-dca, for the first time, as a selective catalyst to reduce CO2 to CO in the presence of a ruthenium photosensitizer (Ru PS) under visible light irradiation. Co-dca was prepared by a facile precipitation method and characterized by Infrared, UV-Vis, XRD, SEM, TEM, and XPS studies. A series of photocatalytic experiments under various reaction conditions were performed to reveal the role of the PS, the scavenger, and the solvent in the selectivity and the activity of the photocatalytic process. We find that Co-dca exhibits an activity of 254 μmol h−1 g−1 and a CO selectivity as high as 93%.

3-Dimensional (3D) cyanide coordination polymers, typically known as Prussian blue Analogues (PBAs), have received great attention in catalysis due to their stability, easily tuned metal sites, and porosity. However, their high crystallinities and relatively low number of surface-active sites significantly hamper their intrinsic catalytic activities. Herein, we report the utilization of a 2-dimensional (2D) layered cobalt tetracyanonickelate, [Co–Ni], for the reduction of protons to H2. Relying on its exposed facets, layered morphology, and abundant surface-active sites, [Co–Ni] can efficiently convert water and sunlight to H2 in the presence of a ruthenium photosensitizer (Ru PS) with an optimal evolution rate of 30 029 ± 590 μmol g−1 h−1, greatly exceeding that of 3D Co–Fe PBA [Co–Fe] and Co–Co PBA [Co–Co]. Furthermore, [Co–Ni] retains its structural integrity throughout a 6 hour photocatalytic cycle, which is confirmed by XPS, PXRD, and Infrared analysis. This recent work reveals the excellent morphologic properties that promote [Co–Ni] as an attractive catalyst for the hydrogen evolution reaction (HER).

Strain engineering can endow versatile functions, such as refining d-band center and inducing lattice mismatch, on catalysts for a specific reaction. To this end, effective strain engineering for introducing strain on the catalyst is highly sought in various catalytic applications. Herein, a facile laser ablation in liquid (LAL) strategy is adopted to synthesize gold nanoparticles (Au NPs) with rich compressive strain (Au-LAL) for electrochemical CO

We present a simple and easy-to-scale synthetic method to plug common organic photosensitizers into a cyanide-based network structure for the development of photosensitizer-water oxidation catalyst (PS-WOC) dyad assemblies for the photocatalytic water oxidation process. Three photosensitizers, one of which absorbs red light similar to P680 in photosystem II, were utilized to harvest different regions of the solar spectrum. Photosensitizers are covalently coordinated to CoFe Prussian blue structures to prepare PS-WOC dyads. All dyads exhibit steady water oxidation catalytic activities throughout a 6 h photocatalytic experiment. Our results demonstrate that the covalent coordination between the PS and WOC group not only enhances the photocatalytic activity but also improves the robustness of the organic PS group. The photocatalytic activity of "plug and play" dyads relies on several structural and electronic parameters, including the position of the energy levels of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the PS with respect to the HOMO level of the catalytic site, the intensity and wavelength of the absorption band of the PS, and the number of catalytic sites.

Metal doping has been used as an effective strategy to tune the energy levels of semiconductors. Herein, we dope NiTi layered double hydroxide (NiTi-LDH) with cobalt to prepare a ternary LDH, CoNiTi-LDH, to enhance its photocatalytic performance towards both water oxidation and hydrogen evolution. A CoNiTi-LDH with smaller plate sizes and a higher degree of order is obtained, which allows the band gap to shrink from 2.7 eV to 2.4 eV. CoNiTi-LDH exhibits a photocatalytic water oxidation activity of 366 μmol g−1 h−1, which is more than two times higher than NiTi-LDH (166 μmol g−1 h−1). We observed that appropriate energy levels of CoNiTi-LDH allow it to be an efficient photocatalyst also for hydrogen evolution. We performed detailed characterization studies to elucidate the effect of Co-doping on photocatalytic activity.

For most semiconductors, especially the visible-light-absorbing ones, the carrier diffusion length is significantly shorter than the light penetration depth, limiting their photoactivities. This limitation could be mitigated through the use of subwavelength semiconductor-based metasurfaces and metamaterials. In this paper, a large-scale compatible metasurface photocathode, made of densely packed disordered p-type chromium oxide (CrOX), is developed to be utilized in photoelectrochemical (PEC) hydrogen generation. For this purpose, first, tightly packed random Cr nanorods are fabricated using an oblique angle deposition technique. Afterward, an annealing step is applied to the sample to transform these metallic units into a semiconducting p-type CrOX-based metasurface. Based on the experimental characterization results and numerical simulations, the proposed design can provide strong light-matter interactions in an ultra-broadband-wavelength range, mainly due to its multidimensional random geometry and ultrasmall gap sizes. Finally, to substantiate the activity of the CrOXnanorods, a core-crown geometry is developed where the NiOXcapping layer catalyzes the hydrogen evolution reaction (HER). The proposed heterostructure metasurface absorber can impose photocurrent values as large as 50 μA cm-2with a photocurrent spectral response extended up to 500 nm. Moreover, the electrode shows outstanding operation under light irradiation for 9 hours. This work demonstrates a simple, scalable design strategy to fabricate low-cost and stable photocathodes for PEC hydrogen evolution. © 2022 American Chemical Society. All rights reserved.

The elucidation of the ideal coordination environment of a catalytic site has been at the heart of catalytic applications. Herein, we show that the water oxidation activities of catalytic cobalt sites in a Prussian blue (PB) structure could be tuned systematically by decorating its coordination sphere with a combination of cyanide and bidentate pyridyl groups. K-0.1[Co(bpy)](2.9)[Fe(CN)(6)](2) ([Cobpy-Fe]), K-0.2[Co(phen)](2.8)[Fe(CN)(6)](2) ([Cophen-Fe]), {[Co(bpy)(2)](3) [Fe(CN)(6)](2) 1[Fe(CN)(6)](1/3) ([Cobpy2-Fe]), and {[Co(phen)(2)](3)[Fe(CN)(6)](2)}[Fe(CN)(6)](1/3) CI0.11 ([Cophen2 - Fe]) were prepared by introducing bidentate pyridyl groups (phen: 1,10-phenanthroline, bpy: 2,2'-bipyridine) to the common synthetic protocol of Co-Fe Prussian blue analogues. Characterization studies indicate that [Cobpy2-Fe] and [Cophen2-Fe] adopt a pentanu- clear molecular structure, while [Cobpy-Fe] and [Cophen-Fe] could be described as cyanide-based coordination polymers with lower-dimensionality and less crystalline nature compared to the regular Co-Fe Prussian blue analogue (PBA), K0.1Co2.9[Fe(CN)(6)](2)([Co-Fe]). Photocatalytic studies reveal that the activities of [Cobpy-Fe] and [Cophen-Fe] are significantly enhanced compared to those of [Co-Fe], while molecular [Cobpy2-Fe] and [Cophen2-Fe] are inactive toward water oxidation. [Cobpy-Fe] and [Cophen-Fe] exhibit upper-bound turnover frequencies (TOFs) of 1.3 and 0.7 s(-1), respectively, which are similar to 50 times higher than that of [Co-Fe] (1.8 X 10(-2) s(-1)). The complete inactivity of [Cobpy2-Fe] and [Cophen2-Fe] confirms the critical role of aqua coordination to the catalytic cobalt sites for oxygen evolution reaction (OER). Computational studies show that bidentate pyridyl groups enhance the susceptibility of the rate-determining Co(IV)-oxo species to the nucleophilic water attack during the critical O-O bond formation. This study opens a new route toward increasing the intrinsic water oxidation activity of the catalytic sites in PB coordination polymers.

The frequent detection of physiological glucose levels from human blood or sweat requires the development of low-cost electrodes with high sensitivity and selectivity. In this work, we prepared a series of Prussian blue (PB) modified carbon cloth (CC) electrodes with different cyanoferrate groups. We achieved a sensitivity as high as 145.43 μA mm−1cm−2 in a 0.1–6.5 mm concentration range with a response time below 2 s under physiological pH. The electrodes exhibited a superior selectivity of glucose in the presence of interfering agents, including sucrose, lactose, NaCl, ascorbic acid, and uric acid. The electrodes also showed outstanding long-term stability over 15 days. Furthermore, we performed comprehensive electrochemical and characterization studies to elucidate the role of the cyanoferrate group on the morphologic and electronic properties of non-enzymatic glucose sensors.

A semiconductor–catalyst hybrid assembly for photocatalytic water oxidation was obtained by preparing CoFe Prussian blue particles on Dion–Jacobson type niobate nanosheets, which produces a p–n junction, as evidenced by the Mott–Schottky plot. The hybrid material with a precious-metal-free cocatalyst exhibits an enhanced photocatalytic activity (89.5 μmol g–1 h–1) in the presence of S2O82– as the electron scavenger. XPS, infrared, XRD, TEM, and SEM studies performed on both pristine and postcatalytic samples indicate that the hybrid assembly exhibits a proper band energy alignment for the photocatalytic water oxidation process and it is stable throughout a 12 h photocatalytic study.

Potassium Nickel hexacyanoferrate Prussian Blue Analogues (K-NiFe-PBAs) offer an excellent platform for efficient CO2 capture due to their porous nature and accessible channels. Herein, the effect of Ni:K atomic ratio on the structure and the CO2 storage capacity was studied by employing K-NiFe-PBAs with Ni:K ratio of ca. 2.5 and 12. The porosity and the isosteric heat of CO2 adsorption can be modulated and optimized by varying the Ni:K atomic ratio in the PB framework and thus, covering the thermodynamic criterion for easy CO2capture and release with acceptable energy costs. The synthesized K-NiFe-PBAs containing only trace amounts of K+ ions (with Ni:K = 12) shows an adsorption capacity (∼3.0 mmol g–1 CO2 at 273 K and 100 kPa) comparable to other well established CO2 adsorbents. In situ FTIR spectroscopy was further employed to elucidate the host–guest interaction chemistry and the dynamics of K-NiFe-PBAs within CO2 and H2O. The analysis enabled, to the best of our knowledge, is the first FTIR spectroscopic observation of the high sensitivity of the material to structural distortions induced by small changes under water vapor pressure. It was found that H2O hardly affects CO2 adsorption and the materials are perspective for CO2 capture in the presence of water.

Nickel oxide (NiO) thin film with a high surface area is an important material in electrochemical applications. Spin coating of a preformed clear solution of ethanol, nickel nitrate, and surfactants (C12H25(OCH2CH2)(10)OH, C12E10 and C16H33N(CH3)(3)Br, CTAB) over a substrate produces a lyotropic liquid crystalline phase that is calcined into a transparent mesoporous NiO (m-NiO) thin film with a uniform film morphology and high porosity and surface area. m-NiO, coated over FTO glass, can be used as an electrode in an electrochromic device and electrocatalytic water oxidation processes with excellent efficiency (Tafel slope of 62 mV dec(-1) and a low overpotential of 0.200 V at 1 mA cm(-2) current density). Repetitive cyclic voltammetry and chronopotentiometry measurements convert the NiO pore walls into a NiO/Ni(OH)(2) core-shell structure. In the water oxidation process, various Ni2+ surface species on the pore-walls are oxidized to Ni3+ and further to Ni4+ electrocatalytic active species. In an electrochromic device, the oxidation of the Ni2+ species to Ni3+ species reversibly contributes to the electrochromic behaviour, but if the electrochromic device is run at more positive potentials (such as those beyond water oxidation potentials), then electrochromic switching takes place between the Ni(OH)(2) and NiOOH surface species.

One of the most critical steps in the transition to carbon-free energy systems is sustainable hydrogen evolution from water. In this research, a cobalt borophosphate crystalline compound consisting of phosphate and borate anions was synthesized with a solid-state reaction. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and X-ray Photoelectron (XPS) was employed to investigate the structure, composition, and morphology of Co3BPO7. Electrocatalytic performances of the catalyst towards oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) have been investigated on nickel foam (NF) electrode in 1.0 M KOH (pH 13.6) by linear sweep voltammetry, chronopotentiometry, cyclic voltammetry, and electrochemical impedance spectroscopy. For OER, the catalyst exhibits an overpotential of 230 mV at 10 mA cm−2 with a Tafel slope of 130 mV dec−1, which is comparable to that of the benchmark RuO2 electrocatalyst, and 220 mV overpotential for a current density of 10 mA cm−2 with a Tafel slope of 147 mV dec−1 for HER process. Long-term chronoamperometry and multiple cyclic voltammetric experiments indicate the catalyst is stable throughout both HER and OER processes. Electrochemical experiments and characterization studies performed on the pristine and post-catalytic electrode indicate that the catalyst is robust under alkaline electrocatalytic conditions (pH 13.6).

Summary The realization of high-performance, precious-metal-free, stable, and robust photoanodes for water oxidation is one of the bottlenecks for dye-sensitized water splitting. Herein, we integrate an organic photosensitizer, which absorbs visible light above 500 nm, with a Prussian blue (PB) network to sensitize a visible-light-absorbing semiconductor, WO3. Through comprehensive steady-state and ultrafast transient absorption studies, we show that the coupling of a photosensitizer to a catalyst through a short cyanide bridging group in a PB structure generates appropriate energy levels for an efficient charge transfer from the photosensitizer to the visible-light-absorbing semiconductor. The photoanode retains its structural integrity and high photoelectrochemical activity for at least 2 h of solar irradiation under mildly acidic conditions (pH 3), which reaches around 1.30 mA/cm2 at 1.23 VRHE. This work provides a simple recipe with a toolbox that can be extended to a variety of organic photosensitizers and semiconductors.

A new composite from graphene quantum dots (GQDs) and NiFe layered double hydroxide was successfully prepared by the coprecipitation method under optimal conditions. The nanoparticles of the composite were analyzed by X‐ray diffraction (PXRD), Fourier transform infrared spectroscopy (FT‐IR), scanning electron microscopy (SEM), and thermal gravimetric analysis (TGA) to obtain the structure, composition and morphology information. Also, the electrochemical properties were investigated by cyclic voltammetry, galvanostatic charge/discharge measurements, and electrochemical impedance spectroscopy. The nanocomposite displays a specific capacitance of 712.7 F g−1 and excellent cycle life after 2500 cycles by applying 10 A g−1 of the current density in 1 M KOH electrolyte, which confirms that the nanocomposite has superb capacitance retention (∼94.8 %) and can be used as a capable supercapacitor. Furthermore, this study provides a desirable procedure for the preparation of novel nanocomposites based on graphene quantum dots, which can be used in energy storage/conversion devices.

A recently emerging visible light-absorbing semiconductor, brown TiO

A recently emerging visible light-absorbing semiconductor, brown TiO2 (b-TiO2), was coupled with a CoFe Prussian blue (PB) analogue to prepare an entirely earth-abundant semiconductor/water oxidation catalyst hybrid assembly. PB/b-TiO2 exhibits a sevenfold higher photocatalytic water oxidation activity compared to b-TiO2. An elegant band alignment unified with the optical absorption of b-TiO2 and excellent electronic dynamics of PB yield a high-performance photocatalytic system.

The development of earth‐abundant photocatalytic assemblies has been one of the bottlenecks for the advancement of scalable water splitting cells. In this study, a ZnCr layered double hydroxide and a CoFe Prussian blue analogue are combined to afford an earth‐abundant photocatalytic assembly involving a visible light‐absorbing semiconductor (SC) and a water oxidation catalyst (WOC). Compared to bare ZnCr‐LDH, the SC‐WOC hybrid assembly exhibits a threefold enhancement in photocatalytic activity, which is maintained for 6 h under photocatalytic conditions at pH 7. The band energy diagram was extracted from optical and electrochemical studies to elucidate the origin of the enhanced photocatalytic performance. This study marks a straightforward pathway to develop low‐cost and precious metal‐free assemblies for visible light‐driven water oxidation.

Prussian blue (PB) and its analogues (PBAs) have at least a three-century-long history in coordination chemistry. Recently, cobalt-based PBAs have been acknowledged as efficient and robust water oxidation catalysts. Given the flexibility in their synthesis, the structure and morphology of cobalt-based PBAs have been modified for enhanced catalytic activity under electrochemical (EC), photocatalytic (PC), and photoelectrochemical (PEC) conditions. Here, in this review, the work on cobalt-based PBAs is presented in four sections: i) electrocatalytic water oxidation with bare PBAs, ii) photocatalytic processes in the presence of a photosensitizer (PS), iii) photoelectrochemical water oxidation by coupling PBAs to proper semiconductors (SCs), and iv) the utilization of PBA-PS assemblies coated on SCs for the dye-sensitized photoelectrochemical water oxidation. This review will guide readers through the structure and catalytic activity relationship in cobalt-based PBAs by describing the role of each structural component. Furthermore, this review aims to provide insight into common strategies to enhance the catalytic activity of PBAs.

A facial and large-scale compatible fabrication route is established, affording a high-performance heterogeneous plasmonic-based photoelectrode for water oxidation that incorporates a CoFe-Prussian blue analog (PBA) structure as the water oxidation catalytic center. For this purpose, an angled deposition of gold (Au) was used to selectively coat the tips of the bismuth vanadate (BiVO

Herein, we establish a simple synthetic strategy affording a heterogeneous, precious metal-free, dye-sensitized photoelectrode for water oxidation, which incorporates a Prussian blue (PB) structure for the sensitization of TiO2 and water oxidation catalysis. Our approach involves the use of a Fe(CN)(5) bridging group not only as a cyanide precursor for the formation of a PB-type structure but also as an electron shuttle between an organic chromophore and the catalytic center. The resulting hetero-functional PB-modified TiO2 electrode demonstrates a low-cost and easy-to-construct photoanode, which exhibits favorable electron transfers with a remarkable excited state lifetime on the order of nanoseconds and an extended light absorption capacity of up to 500 nm. Our approach paves the way for a new family of precious metal-free robust dye-sensitized photoelectrodes for water oxidation, in which a variety of common organic chromophores can be employed in conjunction with CoFe PB structures.

In this paper, we demonstrate a highly efficient light trapping design that is made of a metal-oxide-semiconductor-semiconductor (nanograting/nanopatch) (MOSSg/p) four-layer design to absorb light in a broad wavelength regime in dimensions smaller than the hole diffusion length of the active layer. For this aim, we first adopt a modeling approach based on the transfer matrix method (TMM) to find out the absorption bandwidth (BW) limits of a simple hematite (α-Fe2O3)-based metal-oxide-semiconductor (MOS) cavity design. Our modeling findings show that this design architecture can provide near-perfect absorption in shorter wavelengths. To extend the absorption toward longer wavelengths, a nanostructured semiconductor is placed on top of this MOS design. This nanostructure supports the Mie resonance and adds a new resonance in longer wavelengths without disrupting the lower wavelength absorption capability of MOS cavity. By this way, a polarization-insensitive absorption above 0.8 can be acquired up to λ=565 nm. Moreover, to have a better qualitative comparison, the water-splitting photocurrent of this design has been estimated. Our calculations show that a photocurrent as high as 10.6 mA cm−2 can be achieved with this design that is quite close to the theoretical limit of 12.5 mA cm−2 for hematite-based water-splitting photoanode. This paper proposes a design approach in which the superposition of cavity modes and Mie resonances can lead to a broadband, polarization-insensitive, and omnidirectional near-perfect light absorption in dimensions smaller than the carrier’s diffusion length. This can be considered as a winning strategy to design highly efficient and ultrathin optoelectronic designs in a variety of applications including photoelectrochemical water splitting and photovoltaics.

A facial and large-scale compatible fabrication route is established, affording a high-performance heterogeneous plasmonic-based photoelectrode for water oxidation that incorporates a CoFe-Prussian blue analog (PBA) structure as the water oxidation catalytic center. For this purpose, an angled deposition of gold (Au) was used to selectively coat the tips of the bismuth vanadate (BiVO4 ) nanostructures, yielding Au-capped BiVO4 (Au-BiVO4 ). The formation of multiple size/dimension Au capping islands provides strong light-matter interactions at nanoscale dimensions. These plasmonic particles not only enhance light absorption in the bulk BiVO4 (through the excitation of Fabry-Perot (FP) modes) but also contribute to photocurrent generation through the injection of sub-band-gap hot electrons. To substantiate the activity of the photoanodes, the interfacial electron dynamics are significantly improved by using a PBA water oxidation catalyst (WOC) resulting in an Au-BiVO4 /PBA assembly. At 1.23 V (vs. RHE), the photocurrent value for a bare BiVO4 photoanode was obtained as 190 μA cm-2 , whereas it was boosted to 295 μA cm-2 and 1800 μA cm-2 for Au-BiVO4 and Au-BiVO4 /PBA, respectively. Our results suggest that this simple and facial synthetic approach paves the way for plasmonic-based solar water splitting, in which a variety of common metals and semiconductors can be employed in conjunction with catalyst designs., Scientific and Technological Research Council of Turkey (TÜBİTAK); DPT-HAMIT; Turkish Academy of Sciences; TÜBA-GEBİP for Young İnvestigator Award; BAGEP for Young Scientist Award

In this paper, a visible light driven plasmonic based photoelectrochemical water splitting (PEC-WS) cell is designed with an elegant two-step fabrication route. First, titanium dioxide (TiO2) nanowires (NWs) were synthesized using the hydrothermal method. Then, angled deposition was used to selectively coat the tips of the NWs yielding Au-capped TiO2 NWs with multiple sizes and shapes. The provided randomness leads to a multi-resonant system where the superposition of these resonance modes leads to an overall broadband absorption. The excited localized surface resonance (LSPR) modes contribute to the performance enhancement of the cell via near field effects and a hot electron injection mechanism. Moreover, these nanotips can trigger the formation of Fabry-Pérot (FP) cavity modes. The combination of the above-mentioned mechanisms leads to a high performance visible light driven plasmonic cell. At an applied potential of 1.23 V vs RHE, a photocurrent value as high as 82 μA/cm2 is acquired for the plasmonic based photoanode. The proposed design strategy is a large scale compatible route with no material restriction. Therefore, vast variety of semiconductor-metal pairs can be fabricated to obtain highly efficient water splitting cell for hydrogen generation. This work is supported by the Scientific and TechnologicalResearch Council of Turkey (TUBITAK), grant number215Z249. This work is supported by the project DPT-HAMIT aswell as TUBITAK under the project nos. 113E331, 114E374, and115F560

An entirely earth-abundant chromophore-relay water oxidation catalyst triad system, which is robust and efficient at neutral pH, is presented. The synthesis involves the coordination of a porphyrin derivative to a bridging Fe(CN)5 group, which is then reacted with Co ions to prepare a covalently linked chromophore-Prussian blue analogue assembly. Light-driven water oxidation studies in the presence of an electron scavenger indicate that the triad is active and it maintains a steady activity for at least three hours. Transient absorption experiments and computational studies reveal that the Fe(CN)5 group is more than a linker as it takes part in electron-transfer and co-operates with porphyrin in the charge separation process. This work is supported by the Scientific and Technological Research Council of Turkey (TUBITAK), grant number 215Z249. F.K. and Y.D. thank TÜBA-GEBİP for young investigator awards and BAGEP for a young scientist award.

A facile synthetic pathway using poly(4-vinylpyridine) as a polypyridyl platform is reported for the formation of a metallopolymer. Electrochemical studies indicate that the metallopolymer acts as an efficient H2 evolution catalyst similar to cobalt polypyridyl complexes. It is also observed that the metallopolymer is transformed to cobalt particles when a cathodic potential is applied in the presence of an acid. Electrochemical measurements indicate that an FTO electrode coated with these cobalt particles also acts as an efficient hydrogen evolution catalyst. Approximately 80 µmoles of H2 gas can be collected during 2 h of electrolysis at − 1.5 V (vs. Fc+/0) in the presence of 60 mM of acetic acid. A comprehensive study of the electrochemical and electrocatalytic behavior of cobalt-poly(4-vinylpyridine) is discussed in detail. Graphical Abstract: Poly(4-vinylpyridine) as a precursor for electrodeposited cobalt particles: a cobalt coat derived by a metallopolymer acts as an efficient H2 evolution catalyst. It can transform to a cobalt coat when a potential above − 1.1 V is applied in acid medium. Exchange current density of 10−2.67 mA cm−2 was observed from the Co-coat at − 1.5 V (vs. Fc+/0). Acknowledgements The authors thank the Science and Technology Council of Turkey, TUBITAK (Project No: 215Z249) for financial support. Emine Ülker thanks TUBITAK for support (Project No: 1929B011500059).

Mesoporous, highly active, robust, and cost-effective thin films are in big demand for water splitting by electrocatalysis. Molten-salt assisted self-assembly (MASA) is an effective method to synthesize mesoporous thin films. Transparent clear solutions of salts (LiNO3 and [Mn(H2O)6](NO3)2), acid (HNO3), and surfactants (CTAB and P123) can be spin-coated over substrates as liquid crystalline (LC) films and calcined to obtain mesoporous high quality transparent thin films. A mixture of three salts (LiNO3, [Mn(H2O)6](NO3)2, and [Co(H2O)6](NO3)2) also forms LC mesophases that can be calcined to produce mesoporous nanocrystalline mixed metal lithiates (meso-LiMn2-xCoxO4) with surface areas as large as 144 m2 g-1 (for LiMn1.5Co0.5O4). The synergic effects of these salts improve the pore-size of the final products; the pore size drops from around 11 nm (in the meso-LiMn2O4) to 6-7 nm in the meso-LiMn1-xCoxO4. The meso-LiMn2-xCoxO4 films were tested at pH 13.6 as water oxidation electrocatalysts over a broad range of x. While meso-LiMn2O4 shows a low activity towards water oxidation, the catalytic activity increases with the increasing Co(iii) content of the films. The highest mass activity per cobalt, 1744 A g-1, is obtained for meso-LiMnCoO4, which remains as a robust and efficient film even at a current density of 120 mA cm-2 We thank the Scientic and Technological Research Council of Turkey (TÜBİTAK) under project number 113Z730 for the financial support. Ö. D. is a member of the Science Academy, Istanbul.

A CoFe Prussian blue analogue (CoFe PB) modified FTO electrode, prepared via a facile electrodeposition method, is investigated as a non-enzymatic glucose sensor under neutral conditions. The electrode exhibits a linear detection of glucose in the 0.1–8.2 mmol/L range with a detection limit of 67 μM, a sensitivity of 18.69 μA/mM.cm2, and a fast response time of less than 7 s under neutral conditions. Its stability is confirmed with both electrochemical experiments and characterization studies performed on the pristine and post-mortem electrode. We also conducted a comprehensive electrochemical analysis to elucidate the identity of the active site and the glucose oxidation mechanism on the Prussian blue surface.

A facile synthesis for a photosensitizer-water oxidation catalyst (PS-WOC) dyad, which is connected through a polymeric platform, has been reported. The dyad assembly consists of a ruthenium-based chromophore and a cobalt-iron pentacyanoferrate coordination network as the water oxidation catalyst while poly(4-vinylpyridine) serves as the bridging group between two collaborating units. Photocatalytic experiments in the presence of an electron scavenger reveal that the dyad assembly maintains its activity for 6 h while the activity of a cobalt hexacyanoferrate and Ru(bpy)(3)(2+) couple decreases gradually and eventually decays after a 3 h catalytic experiment. Infrared and XPS studies performed on the post-catalytic powder sample confirm the stability of the dyad during the catalytic process.

The replacement of traditional ruthenium-based photosensitizers with low-cost and abundant iron analogs is a key step for the advancement of scalable and sustainable dye-sensitized water splitting cells. In this proof-of-concept study, a pyridinium ligand coordinated pentacyanoferrate(II) chromophore is used to construct a cyanide-based CoFe extended bulk framework, in which the iron photosensitizer units are connected to cobalt water oxidation catalytic sites through cyanide linkers. The iron-sensitized photoanode exhibits exceptional stability for at least 5 h at pH 7 and features its photosensitizing ability with an incident photon-to-current conversion capacity up to 500 nm with nanosecond scale excited state lifetime. Ultrafast transient absorption and computational studies reveal that iron and cobalt sites mutually support each other for charge separation via short bridging cyanide groups and for injection to the semiconductor in our proof-of-concept photoelectrochemical device. The reorganization of the excited states due to the mixing of electronic states of metal-based orbitals subsequently tailor the electron transfer cascade during the photoelectrochemical process. This breakthrough in chromophore-catalyst assemblies will spark interest in dye-sensitization with robust bulk systems for photoconversion applications.

Non-oxide cobalt based water oxidation electrocatalysts have received attention recently for their relative ease in preparation since they are easy to prepare, stable both in acidic & basic media, and they have higher turnover frequencies compared to cobalt oxides. Recent studies show that one of the main bottlenecks in implementing non-oxide systems to water splitting is the low number of active metal sites, which is in the order of nmol.cm−2. Herein a new series of non-oxide water oxidation catalysts have been introduced to the field. Cobalt dicyanamides are observed to have around four times higher surface active sites and better catalytic performances than cyanide based systems. Long term catalytic studies (70 h) at an applied potential of 1.2 V and electrochemical studies performed in solutions in pHs ranging from 3.0 to 12.0 indicate that the compounds are robust and retain their structures even under drastic conditions. Moreover, addition of nickel impurities to cobalt dicyanamides has been introduced as a feasible method to improve their catalytic activities.

Co/Fe Prussian Blue coordination networks have recently been investigated for heterogeneous water oxidation catalysis. Despite their robustness and stability in both acidic and neutral media, the relatively low current density obtained is their main drawback as a result of their low surface concentration. A novel synthetic approach was employed using a pentacyanometalate-based metallopolymer for the preparation of amorphous Co/Fe coordination polymers to overcome this problem. The surface concentration was improved approximately 7-fold, which also resulted in an increase in the catalytic activity. A current density of 1 mA center dot cm-2 was obtained only at eta = 510 mV, while the same current density could be obtained at higher overpotentials (>600 mV) with conventional Prussian Blue analogues. IR, X-ray photoelectron spectroscopy, and energy-dispersive X-ray spectroscopy studies were performed to investigate the stability of electrodes before and after the electrocatalytic process. The results of this study indicate that the rich and diverse chemistry of pentacyanometalates makes them potential candidates for application in heterogeneous water oxidation catalysis.