Browsing by Subject "Electrocatalysis"

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Open Access
Atomic layer deposition of Pd nanoparticles on N-Doped electrospun carbon nanofibers: optimization of ORR activity of Pd-Based nanocatalysts by tuning their nanoparticle size and loading
(Wiley-VCHVerlagGmbH& Co. KGaA,Weinheim, 2019) Khalily, Mohammad Aref; Patil, Bhushan; Yılmaz, Eda; Uyar, Tamer
Optimization of size, loading and chemical composition of catalytic nanoparticles is a crucial step to achieve cost‐effective and efficient (electro) catalysts. This report elaborates optimization of palladium (Pd) nanoparticle size and loading on the electrospun based N‐doped carbon nanofibers (nCNF) towards oxygen reduction reaction (ORR) for the energy devices like fuel cell, metal air batteries. Electrospinning was utilized to produce one‐dimensional (1D) polyacrylonitrile nanofibers followed by a two‐step carbonization process obtaining well‐defined conductive nCNF having diameters in the range of 200–350 nm. As‐synthesized nCNF was decorated with discrete Pd nanoparticles ranging from 2.6±0.4 nm to 4.7±0.5 nm via thermal atomic layer deposition (ALD) technique. We found that nCNF deposited Pd nanoparticles having 3.9±0.6 nm size (Pd20/nCNF) showed the best ORR activity with the smallest Tafel slope of 58 mV dec−1 along with four electrons involved in the ORR. In addition, high value at half wave potential (E1/2=806 mV vs. RHE) and exchange current densities (i0=6.998 mA cm−2) at Pd20/nCNF makes it efficient catalyst among other Pd decorated nCNF. Moreover, we found that electrocatalyst with lower loading/density of Pd nanoparticles showed enhanced ORR activity.
Open Access
Catalysis with engineered Prussian blue analogues under external bias, light, and magnetic field
(2022-07) Oglou, Ramadan Chalil
The design of robust and feasible catalysts is one of the main concerns towards a carbon emission-free world. Prussian blue analogues (PBAs), the most well-known family of cyanide-based compounds, offer diversity and facile tunability of the structural components to achieve robust catalysts with high selectivities and reproducibilities. Herein this thesis, the catalytic performances of CoFe PBAs have been investigated for glucose and water oxidation processes. The structure of the Prussian blue (PB) framework has been engineered to tune the morphological and electronic properties for enhanced catalytic activity. In this regard, my thesis could be divided into three sections: (i) Electrocatalytic glucose oxidation: In the first part of this study, a CoFe PB modified fluorine-doped tin oxide (FTO) electrode, which is prepared via an electrodeposition method, was investigated as a non-enzymatic glucose sensor under neutral conditions. The electrode exhibits a linear detection of glucose in the 0.1 − 8.2 mM range with a detection limit of 67 μM, and a sensitivity of 18.69 mA mM−1 cm−2. Its stability is confirmed with both electrochemical experiments and characterization studies performed on the pristine and post-mortem electrodes. We also conducted a comprehensive electrochemical analysis to elucidate the identity of the active site and the glucose oxidation mechanism on the PB surface. In the second part, a series of PB modified carbon cloth (CC) electrodes were prepared with different cyanoferrate groups. A sensitivity as high as 145.43 μA mM−1 cm−2 in a 0.1 – 6.5 mM concentration range is achieved with a response time below 2 s under physiological pH. The electrodes exhibit a superior selectivity of glucose in the presence of interfering agents, including sucrose, lactose, sodium chloride, ascorbic acid, and uric acid. The electrodes also show 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. (ii) Photocatalytic water oxidation: 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 PB 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 groups enhances not only the photocatalytic activity but also the robustness of the organic PS group. We find that the photocatalytic activity of these “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. (iii) Intermetallic charge transfer induced electrocatalysis: We report a novel route to enhance the sluggish kinetics of oxygen evolution reaction (OER) by manipulating the intermetallic charge transfer (IMCT) of PBAs. It is found that CoFe PBAs with dissimilar charge transfer abilities reveal a positive response for OER under external stimuli such as magnetic field and light illumination, in which the magnitude of enhancement can be correlated to the intensity of metal-to-metal charge transfer (MMCT) profiles rather than the catalytic activity. An enhancement of almost 57% for OER activity is observed under a 1 h light irradiation for the CoFe PBA that exhibits the strongest IMCT nature. Several control experiments are conducted correlating the direct relation of IMCT and external stimuli induced activity involving –electrochemical experiments at varying pH conditions. Overall, this thesis indicates that CoFe PBAs could be engineered to design robust catalysts for oxidation reactions. Furthermore, they could also be fine-tuned to develop catalytic assemblies, which are responsive to applied bias, magnetic field, and light irradiation. Given the previous efforts in employing PBAs for catalytic applications, this thesis pushes the limits one step forward and brings a new level to this challenge.
Open Access
A cyanide-based coordination polymer for hydrogen evolution electrocatalysis
(Springer New York LLC, 2018) Alsaç, Elif Pınar; Ülker, E.; Nune, Satya Vijaya Kumar; Karadaş, Ferdi
Abstract: Research on H2 production has recently been directed to the development of cost-efficient and robust heterogeneous catalysts for hydrogen evolution reaction (HER). Given the promising catalytic activities of several cobalt-based systems and the robustness of Prussian blue analogues in harsh catalytic processes including water oxidation, a Co-Co Prussian blue analogue was investigated as a HER catalyst for the first time. Co-Co Prussian Blue modified fluorine doped tin oxide (FTO) electrode demonstrated a significant HER activity with an onset overpotential of 257 mV, a Tafel slope of 80 mV dec−1, and a turnover frequency of 0.090 s−1 at an overpotential of 250 mV. Comparative XPS, Infrared, and XRD studies performed on pristine and post-catalytic electrodes confirm the stability of the catalyst.
Open Access
Development of CuAg/Cu2O nanoparticles on carbon nitride surface for methanol oxidation and selective conversion of carbon dioxide into formate
(Elsevier, 2020) Nazir, Roshan; Kumar, A.; Saad, M. A. S.; Ali, S.
Herein we report a catalyst consisting of CuAg/Cu2O nanoparticles (NPs), synthesized on the two-dimensional carbon nitride (Csingle bondN) surface via galvanic exchange route for electrocatalytic methanol oxidation and carbon dioxide reduction. The lower reduction potential of copper ([Cu+(aq) + e− → Cu(s)], + 0.52 eV) compared to Ag ([Ag+(aq) + e− → Ag(s)], +0.80 eV) makes Cu(0) easily exchangeable by Ag+ ions via galvanic exchange without applying any external bias. In a two-step process, the Cu NPs are synthesized first on Csingle bondN surface by adsorbing Cu2+ precursors and reducing them by NaBH4. Due to unstable nature of Cu2+ in aqueous medium some Cu2O NPs (a mixed phase of Cu/CuO) were also formed. Thereafter in the second step, Ag+ precursors are brought in contact with the already synthesized Cu and Cu2O nanoparticles (NPs). The Cu and Cu2O NPs present on the surface of Csingle bondN are partially exchanged by Ag atoms to generate bimetallic CuAg/Cu2O NPs. Two atoms of Ag are expected to be deposited for every Cu atom replaced. As galvanic replacement occurs on the solid surface of carbon nitride, there is only a partial replacement of Cu and Cu2O atoms. The catalysts Csingle bondN/Cu/Cu2O and Csingle bondN/CuAg/Cu2O were evaluated for their performance towards methanol oxidation and carbon dioxide reduction. Csingle bondN/CuAg/Cu2O showed twice the current density for methanol oxidation than Csingle bondN/Cu/Cu2O in a 0.5 M methanol solution. Probably the reason for high activity of Ag than Cu is related to the weak bond of oxygen on silver substrate for oxidation reactions and strong binding affinity on copper substrate. In case of carbon dioxide reduction (CO2 reduction) the product was identified to be formate by oxidizing the product (formate) on a Pt ring electrode. The results revealed Csingle bondN/CuAg/Cu2O shows a better selectivity towards formic acid formation than Csingle bondN/Cu/Cu2O using the rotating ring disc electrode (RRDE). A probable reason may be the strain induced by alloy formation which could favor a reduced coverage of adsorbed hydrogen and a decrease in oxophilicity of the compressively strained copper.
Open Access
Electrochemically generated catalyst system with increased specificity and efficiency for olefin metathesis
(Elsevier, 2003-11-01) Düz, B.; Pekmez, K.; İmamoğlu, Y.; Süzer, Ş.; Yıldız, A.
A facile route for the electrochemical generation of an olefin metathesis catalyst from methylene chloride solution Of WCl6 was described. It was found that reductive, oxidative and pulse electrolysis produced the same intermediate. This electrolysis intermediate incorporates olefin into its structure possibly forming a metal-olefin complex, which decomposes into catalytically active metal carbene type species. ESCA, NMR and ESR methods were used to elucidate the structure of the catalyst system. The catalyst was applied in the metathesis of 1-octene and 2-octene without any need for a co-catalyst. Highly specific products with high yields were obtained. (C) 2003 Elsevier B.V. All rights reserved.
Open Access
Investigation of electrocatalytic performance of prussian blue analogues for water splitting
(2017-09) Alsaç, Elif Pınar
Research on H2 production has recently been directed to the development of cost-efficient and robust heterogeneous catalysts for splitting of water. While several Prussian blue analogues (PBAs) have been investigated as water oxidation catalysts, the field lacks a comprehensive study that focuses on the design of the ideal PBA for efficient water oxidation. Herein this thesis, a series of PBAs with different cyanide precursors were investigated to study the effect of hexacyanometal group to their electrocatalytic catalytic water oxidation activities. Cyclic voltammetry, chronoamperometry, and chronopotentiometry measurements reveal the close relation between the electron density of electroactive cobalt sites and electrocatalytic activity, which is also confirmed by Infrared and XPS studies. pH dependent cyclic voltammetry studies were also performed to gain insight about the catalytic mechanism and electronic structure of cyanide-based systems, to identify possible intermediates, and assign the rate-determining step of the process. In addition, a N-donor ligand, 1-heptyl 4-(4 pyridyl) pyridinium bromide, was used to prepare a new pentacyanoferrate complex. This complex was used to make a new series of PB analogues to investigate the effect of the change in the morphology to electrocatalytic water oxidation performance. Synthesis, characterization, and electrochemical experiments were performed to investigate electrocatalytic properties of PB analogues. With this synthesis route, the electroactive cobalt sites are increased approximately two-fold. It is observed that amorphous nature has positive impact on the catalytic activity when compared to cobalt hexacyanoferrates. A current density of 1 mA.cm-2 was achieved at an overpotential of 421 mV, which is much lower than those obtained with metal hexacyanometalates. Given the promising catalytic activities of several cobalt-based systems and the robustness of Prussian blue analogues in harsh catalytic processes including water oxidation, a Co-Co Prussian blue analogue was investigated as a Hydrogen evolution catalyst for the first time. Co-Co Prussian Blue modified FTO electrode demonstrated a significant Hydrogen evolution activity with an onset overpotential of 257 mV, a Tafel slope of 80.2 mV.dec-1, and a turnover frequency of 0.090 s-1 at an overpotential of 250 mV. Comparative XPS, Infrared, and XRD studies performed on pristine and post-catalytic electrodes confirm the stability of the catalyst.
Open Access
Investigation of the ideal composition of metal hexacyanocobaltates with high water oxidation catalytic activity
(TÜBİTAK, 2019) Karadaş, Ferdi
The electrocatalytic activities of Prussian blue analogues (PBAs) have recently received much attention due to their robustness and efficiency. Considering that PBAs with hexacyanocobaltate building block stand forward among other PBAs, a systematic study on a family of metal hexacyanocobaltates is presented in this study. Metal hexacyanocobaltates (M = Co, Mn, Ni, and Fe) were prepared, characterized, and electrochemical studies were performed. A series of mixed-metal cobalt-iron hexacyanocobaltates has also been studied to determine the ideal composition of a metal hexacyanocobaltate for electrocatalytic water oxidation process. The overall study clearly indicates that cobalt hexacyanocobaltate exhibits the highest electrocatalytic activity among all.
Open Access
Manipulating intermetallic charge transfer for switchable external stimulus-enhanced water oxidation electrocatalysis
(John Wiley and Sons Inc, 2023-10-26) Chalil Oglou, Ramadan; Ulusoy Ghobadi, Türkan Gamze; Hegner, F. S. .; Galán-Mascarós, J. R.; López, N; Özbay, Ekmel; Karadaş, Ferdi
Electrocatalytic processes involving the oxygen evolution reaction (OER) present a kinetic bottleneck due to the existence of linear-scaling relationships, which bind the energies of the different intermediates in the mechanism limiting optimization. Here, we offer a way to break these scaling relationships and enhance the electrocatalytic activity of a Co−Fe Prussian blue modified electrode in OER by applying external stimuli. Improvements of ≈11 % and ≈57 % were achieved under magnetic field (0.2 T) and light irradiation (100 mW cm−2), respectively, when working at fixed overpotential, η=0.6 V at pH 7. The observed enhancements strongly tie in with the intermetallic charge transfer (IMCT) intensity between Fe and Co sites. Density Functional Theory simulations suggest that tuning the IMCT can lead to a change of the OER mechanism to an external stimuli-sensitive spin crossover-based pathway, which opens the way for switchable electrocatalytic devices.
Open Access
Mesoporous MnCo2O4 NiCo2O4 and ZnCo2O4 thin-film electrodes as electrocatalysts for the oxygen evolution reaction in alkaline solutions
(American Chemical Society, 2021-03-22) Amirzhanova, Assel; Akmanşen, Nesibe; Karakaya, Irmak; Dağ, Ömer
The oxygen evolution reaction (OER) is the bottleneck of the electrochemical water-splitting process, where the use of porous metal oxide electrodes is beneficial. In this work, we introduce a one-pot synthesis method to fabricate a series of mesoporous metal cobaltite (m-MCo2O4, M = Mn, Ni, and Zn) electrodes for the OER. The method involves preparation and coating of a homogeneous clear solution of all ingredients (metal salts and surfactants) over a fluorine-doped tin oxide surface as a thin lyotropic liquid crystalline film and calcination (as low as 250 °C) to obtain a 400 nm thick crystalline m-MCo2O4 electrode with a spinel structure. Mesophases and m-MCo2O4 films are characterized using structural and electrochemical techniques. All electrodes are stable during the electrochemical test in 1 M KOH aqueous solution and perform at as low as 204 mV overpotential at 1 mA/cm2 current density; the m-MnCo2O4 electrode works at current densities of 1, 10, and 100 mA/cm2 at 227, 300, and 383 mV overpotentials after compensating the IR drop, respectively. The Tafel slope is 60 mV/dec for the m-NiCo2O4 and m-ZnCo2O4 electrodes, but it gradually increases to 85 mV/dec in the m-MnCo2O4 electrode by thermal treatment, indicating a change in the OER mechanism.
Open Access
Molten salt assisted self-assembly: synthesis of mesoporous LiCoO2 and LiMn2O4 thin films and investigation of electrocatalytic water oxidation performance of lithium cobaltate
(Wiley-VCH Verlag, 2018) Saat, G.; Balci, F. M.; Alsaç, E. P.; Karadas, F.; Dağ, Ömer
Mesoporous thin films of transition metal lithiates (TML) belong to an important group of materials for the advancement of electrochemical systems. This study demonstrates a simple one pot method to synthesize the first examples of mesoporous LiCoO2 and LiMn2O4 thin films. Molten salt assisted self-assembly can be used to establish an easy route to produce mesoporous TML thin films. The salts (LiNO3 and [Co(H2O)6](NO3)2 or [Mn(H2O)4](NO3)2) and two surfactants (10-lauryl ether and cethyltrimethylammonium bromide (CTAB) or cethyltrimethylammonium nitrate (CTAN)) form stable liquid crystalline mesophases. The charged surfactant is needed for the assembly of the necessary amount of salt in the hydrophilic domains of the mesophase, which produces stable metal lithiate pore-walls upon calcination. The films have a large pore size with a high surface area that can be increased up to 82 m2 g−1. The method described can be adopted to synthesize other metal oxides and metal lithiates. The mesoporous thin films of LiCoO2 show promising performance as water oxidation catalysts under pH 7 and 14 conditions. The electrodes, prepared using CTAN as the cosurfactant, display the lowest overpotentials in the literature among other LiCoO2 systems, as low as 376 mV at 10 mA cm-2 and 282 mV at 1 mA cm-2.
Open Access
Nanoarchitectonics of mesoporous CaFe2O4 thin-film electrodes from salt-surfactant lyotropic liquid crystalline mesophases and their OER performance
(American Chemical Society, 2023-09-05) Raza, Hamid Ali; Karakaya, Irmak; Dağ, Ömer
Metal oxides of earth-abundant elements (such as Ca and Fe) are highly important for fabricating active electrodes for various electrochemical applications (such as electrocatalysis and photo-electrocatalysis). Here, we employed a molten-salt-assisted self-assembly process to fabricate CaFe2O4 thin-film electrodes on graphite rods. The roles of precursor type (nitrates and chlorides) and solvent (water and ethanol) have been addressed in the fabrication of the electrodes that are tested in oxygen evolution reaction (OER) in alkali media. The mesophases have an unusual orthorhombic structure that is likely transformed from a well-known 3D hexagonal phase by an elongation along the b-axis caused by the hydrolysis and condensation of the Fe(III) species in the lyotropic liquid crystalline media. Four sets of mesoporous electrodes with a high surface area are fabricated using nitrate and chloride precursors in aqueous media and nitrates in ethanol. The electrodes, fabricated from the chloride precursors, are not as porous as nitrates, but they display better performance in the OER. The electrodes, fabricated from ethanol solutions, outperform, are more robust, and display as low as 250, 342, and 642 mV overpotentials at 1, 10, and 100 mA/cm2 current densities with a Tafel slope of around 60 mV/dec. The electrode thickness has no role in the electrode performance and can be prepared as thin as tens of nanometers with good stability and OER performance.
Open Access
One-dimensional copper (II) coordination polymer as an electrocatalyst for water oxidation
(Wiley-VCH Verlag, 2017) Mishra, R.; Ülker, E.; Karadas, F.
Although cobalt-based heterogeneous catalysts are the central focus in water oxidation research, interest in copper-based water oxidation catalysts has been growing thanks the great abundance of copper and its biological relevance. Several copper oxides have recently been reported to be active catalysts for water oxidation. In this study, a heterogeneous copper-based water oxidation catalyst that is not an oxide has been reported for the first time. Single-crystal XRD studies indicate that the compound is a one-dimensional coordination compound incorporating copper paddle-wheel units connected through phosphine dioxide ligands. The catalyst exhibits an onset potential of 372 mV at pH 10.2, whereas an overpotential of only 563 mV is required to produce a current density of 1 mA cm−2. In addition to cyclic voltammetric and chronoamperometric studies, an investigation into the effect of pH on the catalytic activity and the robustness of the catalyst using long-term bulk electrolysis (12 h) is presented.
Open Access
Synthesis, characterization, and electrochemical properties of mesoporous spinel LiMn2-xMxO4 (M = Mn, Fe, Co, Ni, AND Cu) thin films
(2024-05) Durukan, Irmak Karakaya
Mesoporous LiMn2-xMxO4 electrodes are promising candidates for efficient oxygen evolution (OER) electrocatalysis. In this study, mesoporous LiMn2-xMxO4 (where M is Mn, Fe, Co, Ni, and Cu) thin films have been fabricated by employing molten-salt assisted self-assembly (MASA) method on fluorine doped tin oxide (FTO) surface. The electrodes are characterized according to their structure, morphology, and thicknesses using various characterization techniques. The electrochemical properties of the films are comprehensively investigated under acidic, alkaline, neutral, and non-aqueous solutions. The manganese oxide-based electrodes undergo Mn(III) and Mn(VI) disproportionation reactions. Here, we have extensively investigated these disproportionation reactions by post-characterization techniques after electrochemical experiments using LiMn2-xMxO4 (M is Fe, Co, Ni, and Cu and x is 0, 0.1, 0.3, 0.4, and 0.67) and Mn3O4 electrodes. The LiMn2O4 thin films are found to be more stable in OER compared to Mn3O4. Lithium de-intercalation of the LiMn2O4 films produces a λ-MnO2 phase robust against Mn(VI) disproportionation. The electrochemical degradation rates are investigated using the LiMn2O4 electrodes, fabricated at various spin rates (from 2000 and 10000 rpm). The film thicknesses are between 150 and 500 nm. The LiMn2O4 electrode at 5000 rpm is more resistant to physical degradation during electrochemical tests. Charge capacity values of the thin films are determined by electrochemical experiments in LiNO3 electrolyte and found to be between 136 and 273 mC/cm2 for the films, then these values are used to calculate their approximate weights (between 30 and 60 μg/cm2). The annealing temperature for the LiMn2O4 thin films is also optimized for a stable OER. The LiMn2O4 film, fabricated at 5000 rpm spin rate and annealed at 300 oC, is found to be a more robust and efficient electrode with a 60 mV/dec Tafel slope and 812 mV overpotential at 10 mA/cm2 current density. The same fabrication parameters are used for the other mesoporous LiMn2-xMxO4 thin films. The LiMn2-xMxO4 thin films are used to collect their N2-adsorption-desorption isotherms. The isotherms display type IV hysteresis, characteristic of mesoporous materials. BET surface areas are estimated as 98, 99, 116, 112, and 75 m2/g for the LiMn2O4, LiMn1.7Fe0.3O4, LiMn1.7Co0.3O4, LiMn1.7Ni0.3O4 and LiMn1.7Cu0.3O4, films, respectively. Moreover, the LiMn2-xMxO4 electrodes (fabricated at 5000 rpm spin rate and 300 oC annealing temperature) are investigated for lithium de-intercalation/intercalation behavior in 1 M LiNO3 solution. Then, the same electrodes are used to collect 300 CVs, CAs, and CPs in 1 M KOH solution to evaluate electrochemical behaviors. From these measurements, the origin of phase separation and bearing lower oxidation states of the nickel and copper at higher x values are identified in the spinel structure. The Mn(VI) disproportionation reaction on the LiMn2-xMxO4 electrodes is investigated by CV cycling experiments in 1 M KOH. The LiMn2O4, LiMn2-xFexO4, and LiMn2-xCuxO4 electrodes undergo fast degradation compared to LiMn2-xCoxO4 and LiMn2-xNixO4 through the dispersion of [MnO4]- and [FeO4]2- ions and dissolution of the CuO phase formed in the electrodes during OER. The LiMn1.7M0.3O4 thin films on FTO are used in OER electrocatalysis and the overpotential values at 10 mA/cm2 are evaluated as 645, 686, and 657 mV for the LiMn1.7Fe0.3O4, LiMn1.7Co0.3O4, LiMn1.7Ni0.3O4 electrodes, respectively. The exact compositions are also coated on graphite substrates and their overpotential values are also evaluated as 629, 462, 440, and 532 mV at 10 mA/cm2 for the LiMn2O4, LiMn1.7Fe0.3O4, LiMn1.7Co0.3O4, LiMn1.7Ni0.3O4 electrodes, respectively. The LiMn1.7Co0.3O4 on graphite and LiMn1.7Ni0.3O4 on FTO electrodes are found to be the most robust and efficient electrodes at a 50 mA/cm2 current density.
Open Access
Tuning the electronic properties of prussian blue analogues for efficient water oxidation electrocatalysis: experimental and computational studies
(Wiley-VCH Verlag, 2018) Alsaç, Elif Pınar; Ülker, E.; Nune, Satya Vijaya Kumar; Dede, Y.; Karadaş, Ferdi
Although several Prussian Blue analogues (PBAs) have been investigated as water oxidation catalysts, the field lacks a comprehensive study that focuses on the design of the ideal PBA for this purpose. Here, members of a series of PBAs with different cyanide precursors have been investigated to study the effect of hexacyanometal groups on their electrocatalytic water oxidation activities. Cyclic voltammetric, chronoamperometric, and chronopotentiometric measurements have revealed a close relationship between the electron density of electroactive cobalt sites and electrocatalytic activity, which has also been confirmed by infrared and XPS studies. Furthermore, pH-dependent cyclic voltammetry and computational studies have been performed to gain insight into the catalytic mechanism and electronic structure of cyanide-based systems to identify possible intermediates and to assign the rate-determining step of the target process.
Open Access
Water oxidation electrocatalysis with a cobalt ‐ borate ‐ based hybrid system under neutral conditions
(Wiley-VCH Verlag, 2018) Turhan, Emine A.; Nune, Satya Vijaya Kumar; Ülker, E.; Şahin, U.; Dede, Y.; Karadaş, Ferdi
The development of new water oxidation electrocatalysts that are both stable and efficient, particularly in neutral conditions, holds great promise for overall water splitting. In this study, the electrocatalytic water oxidation performance of a new cobalt-based catalyst, Co3(BO3)2, with a Kotoite-type crystal structure is investigated under neutral conditions. The catalyst is also hybridized with CNTs to enhance its electrocatalytic properties. A remarkable increase in catalytic current along with a significant shift in the onset overpotential is observed in Co3(BO3)2@CNT. Additionally, CNT addition also greatly influences the surface concentration of the catalyst: 12.7 nmol cm−2 for Co3(BO3)2@CNT compared with 3.9 nmol cm−2 for Co3(BO3)2. Co3(BO3)2@CNT demands overpotentials of 303 and 487 mV to attain current densities of 1 and 10 mA cm−2, respectively, at pH 7. Electrochemical and characterization studies performed over varying pH conditions reveal that the catalyst retains its stability over a pH range of 3-14. Multi-reference quantum chemical calculations are performed to study the nature of the active cobalt sites and the effect of boron atoms on the activity of the cobalt ions.