Efficient Electrochemical Water Oxidation Research Articles

Efficient electrochemical water oxidation to hydrogen peroxide over intrinsic carbon defect-rich carbon nanofibers

Carbon nanofibers enriched in ring-defects significantly promote electrochemical water oxidation to hydrogen peroxide.

A Cobalt@Cucurbit[5]uril Complex as a Highly Efficient Supramolecular Catalyst for Electrochemical and Photoelectrochemical Water Splitting.

A host–guest complex self‐assembled through Co2+ and cucurbit[5]uril (Co@CB[5]) is used as a supramolecular catalyst on the surface of metal oxides including porous indium tin oxide (ITO) and porous BiVO4 for efficient electrochemical and photoelectrochemical water oxidation. When immobilized on ITO, Co@CB[5] exhibited a turnover frequency (TOF) of 9.9 s−1 at overpotential η=550 mV in a pH 9.2 borate buffer. Meanwhile, when Co@CB[5] complex was immobilized onto the surface of BiVO4 semiconductor, the assembled Co@CB[5]/BiVO4 photoanode exhibited a low onset potential of 0.15 V (vs. RHE) and a high photocurrent of 4.8 mA cm−2 at 1.23 V (vs. RHE) under 100 mW cm−2 (AM 1.5) light illumination. Kinetic studies confirmed that Co@CB[5] acts as a supramolecular water oxidation catalyst, and can effectively accelerate interfacial charge transfer between BiVO4 and electrolyte. Surface charge recombination of BiVO4 can be also significantly suppressed by Co@CB[5].

A Cobalt@Cucurbit[5]uril Complex as a Highly Efficient Supramolecular Catalyst for Electrochemical and Photoelectrochemical Water Splitting

AbstractA host–guest complex self‐assembled through Co2+ and cucurbit[5]uril (Co@CB[5]) is used as a supramolecular catalyst on the surface of metal oxides including porous indium tin oxide (ITO) and porous BiVO4 for efficient electrochemical and photoelectrochemical water oxidation. When immobilized on ITO, Co@CB[5] exhibited a turnover frequency (TOF) of 9.9 s−1 at overpotential η=550 mV in a pH 9.2 borate buffer. Meanwhile, when Co@CB[5] complex was immobilized onto the surface of BiVO4 semiconductor, the assembled Co@CB[5]/BiVO4 photoanode exhibited a low onset potential of 0.15 V (vs. RHE) and a high photocurrent of 4.8 mA cm−2 at 1.23 V (vs. RHE) under 100 mW cm−2 (AM 1.5) light illumination. Kinetic studies confirmed that Co@CB[5] acts as a supramolecular water oxidation catalyst, and can effectively accelerate interfacial charge transfer between BiVO4 and electrolyte. Surface charge recombination of BiVO4 can be also significantly suppressed by Co@CB[5].

Na+-induced in situ reconstitution of metal phosphate enabling efficient electrochemical water oxidation in neutral and alkaline media

Exploring highly activity and stable electrocatalysts for oxygen evolution reaction (OER) is of vital importance for sustainable energy conversion processes. Herein, a facile strategy is developed to synthesize Ni-doped CoOOH nanosheets with poor crystallinity and 3D mesh structure, which is in situ derived from the Na+-induced spontaneous reconstitution of polymetallic phosphate precursors during OER process. The resulted Ni-CoOOH/NF with a large number of active sites exhibits a highly efficient OER catalytic activity outperforming the commercial RuO2 catalysts, indicated by low overpotentials of only 265 and 410 mV at a current density of 10 mA cm−2 in alkaline and neutral media, respectively. This Na+-induced in situ conversion strategy opens up a new way for the design and synthesis of electrocatalysis towards various energy systems.

Electrodeposition of Fe-Group Mutual Alloys for Efficient Electrochemical Water Oxidation

In this work, galvanostatic electrodeposition from an electrolyte without buffers was performed to generate thin films consisting of Ni, Fe and Co on various substrates. The self-limiting behavior was proven by electroplating at different durations, showing that the thickness was unchanged. The growth was self-limiting due to the pH increase, resulting in an outer layer composed of a compact hydroxide/oxyhydroxide. XPS depth profiles confirm the formation of the surface hydroxide/oxyhydroxide. Studies of nucleation dynamics show that these films nucleate slower if the alloy films include more elements. Ni-Co-Fe films deposited on Au were further investigated as electrochemical catalysts in 1M KOH solution for oxygen evolution. All the films exhibit reduced Tafel slopes (34.7 to 38.4 mV/dec) and small onset potentials (0.314 to 0.320 VRHE), implying an enhanced water oxidation kinetics. The optimum deposition time was found to be 1s in terms of the electrochemical catalytic properties, due to a lower thickness of the surface hydroxide/oxyhydroxide layer.

Neutral and alkaline chemical environment dependent synthesis of Mn3O4 for oxygen evolution reaction (OER)

Co-precipitation assisted hydrothermal synthesis was employed to prepare Mn3O4 electrocatalysts for efficient electrochemical water oxidation. Tetragonal structure of high crystalline and pure phase Mn3O4 nanostructures was confirmed by X-ray diffraction (XRD) spectra. Physical characteristics such as vibration, optical and morphology of the electro catalysts were examined and confirmed by Raman spectra, Fourier Transform Infrared Spectra (FTIR), photoluminescence spectra (PL) and ultra-violet diffuse reflection spectra (UV-DRS) respectively. Mn3O4 electro catalysts were deposited on GCE electrode for investigating the electrochemical behavior. The electrochemical water splitting application was demonstrated by the prepared Mn3O4 electro catalysts in conventional three electrode cell with Hg/HgO as a reference electrode and Pt mesh as a counter electrode. Higher current density of 1.31 mA/g with lowest Tafel slope value of 63 mV/dec was achieved for the prepared electro catalyst synthesized in base pH condition. Good stability of 55% over 12 h long time was achieved for the electro catalysts in alkaline medium under continuous electrochemical reaction with good retention in performance. Hence, the controlled alkaline environmentally synthesized Mn3O4 electro catalysts prepared in this work achieved the good standard of highly efficient electrode material for electrochemical water splitting applications.

Electrochemical Water Oxidation of NiCo2O4 and CoNi2S4 Nanospheres Supported on Ni Foam Substrate

AbstractElectrochemical water splitting is an environment‐friendly technique for producing clean energy. Low‐cost, high performance and robust electro catalysts for electrochemical oxygen evolution reaction (OER) is highly essential for improving the overall efficiency of water splitting. In the present study, NiCo2O4 and CoNi2S4 nanospheres were successfully prepared by employing solvothermal method and optimized at 180°C. XRD result confirmed the formation of cubic structure of both NiCo2O4 and CoNi2S4 nanospheres. SEM images evidently revealed the perfect nanospherical surface morphology of NiCo2O4 and distorted nanospherical morphology of CoNi2S4. The obtained characteristic Raman active modes of vibrations confirmed the product formation. Photoluminescence study proclaimed the emission behavior of the product. FTIR results confirmed the metal oxygen vibrations such as Ni−O, Co−O and Ni−S of NiCo2O4 and CoNi2S4 nanospheres. UV spectra and Tauc plot revealed the optical band gaps of Ni and Co based oxide and sulfide nanospheres. Electrochemical studies of optimized NiCo2O4 and CoNi2S4 revealed the respective specific capacitance of 767.067 F/g and 648.11 F/g at scan rate of 10 mVs−1 in 1 M KOH electrolyte solution. Furthermore, the current density of 331 and 159 mAg−1 was achieved for the best performed NiCo2O4 and CoNi2S4 electrodes with improved electrical conductivity. The stability over 12 h of highly performed NiCo2O4 nanospheres has been reported. This work suggested a viable and optimized approach to synthesize Ni and Co based oxide and sulfide nanospheres for efficient electrochemical water oxidation.

Amorphous nickel sulfide nanosheets with embedded vanadium oxide nanocrystals on nickel foam for efficient electrochemical water oxidation

A self-supported hierarchical OER catalyst comprising VO/VO2 nanocrystals embedded in amorphous Ni3S2 nanosheets on Ni foam is reported.

Iron carbonate hydroxide templated binary metal-organic frameworks for highly efficient electrochemical water oxidation.

Metal-organic frameworks (MOFs) are promising catalysts for electrochemical reactions. Herein, self-supported NiFe-MOF nanoplates grown on Ni foam (NF) were prepared with iron carbonate hydroxide nanosheets (FeCH NSs) as a semisacrificial template and evaluated for the electrocatalytic oxygen evolution reaction (OER). In this approach, the porous FeCH NSs not only serve as the iron source of NiFe-MOF, but also slow down the leaching of Ni ions from the substrate, thus playing a unique role in regulating the morphology of NiFe-MOF with reduced thickness and sizes, enabling rapid electron transfer and mass transport. The resultant NiFe-MOF/FeCH-NF electrode showed higher activity than FeCH template-free electrodes and superior OER performance over other MOF based binder-free OER electrodes. A current density of 10 mA cm-2 was obtained at a low overpotential of 200 mV with excellent durability in alkaline solution. Raman and TEM measurements reveal the partial transformation of NiFe-MOF to hydroxide during water oxidation.

Cobalt polyoxometalate-derived CoWO4 oxygen-evolving catalysts for efficient electrochemical and photoelectrochemical water oxidation

Highly efficient water-oxidation catalysts (WOCs) were readily prepared through the simple heat treatment of cobalt-containing polyoxometalate [Co4(H2O)2(PW9O34)2]10− (POM). The annealing of soluble POM molecules at high temperatures in air led to the formation of insoluble nanoparticles, of which the crystal structure and catalytic activity can be controlled by the annealing temperature. POMs were converted to amorphous and crystalline CoWO4 nanoparticles when annealed at 400 and 500 °C, respectively. Interestingly, amorphous CoWO4 nanoparticles exhibited excellent catalytic activity near the neutral pH of pH 8.0, making them superior to both pristine POM and POM-derived crystalline CoWO4 nanoparticles. X-ray absorption and photoelectron spectroscopies combined with density functional theory (DFT) calculations revealed that their outstanding performance was resulted from the generation of large amounts of oxygen vacancies upon annealing, leading to the optimum distance between the nearest Co ions for the Langmuir-Hinshelwood (LH) mechanism. Based on these findings, we could readily immobilize CoWO4-based WOCs on the surfaces of various electrodes for efficient electrochemical and photoelectrochemical water oxidation through the annealing of POMs pre-adsorbed onto the desired electrode surface. This study may provide insights not only for the synthesis of efficient electrocatalysts derived from POMs but also for their immobilization onto the desired electrode surface for practical applications.

Highly dispersed cobalt decorated uniform nitrogen doped graphene derived from polydopamine positioning metal-organic frameworks for highly efficient electrochemical water oxidation

The development of high-performance noble metal-free electrochemical catalyst for effective water splitting is a key factor to achieve low-cost and sustainable renewable energy production. Herein, for the first time, highly dispersed cobalt nanoparticles decorated uniform nitrogen doped graphene (CoNPs-N-GR) was design synthesized. In the preparation procedure, graphene oxide (GO) was employed as supporting material, polydopamine as nitrogen source, location reagent as well as connecting agent for uploading cobalt metal ion, and then cobalt metal-organic frameworks (ZIF-67) in situ grew on GO. During the calcining process, GO reduction, nitrogen doping and cobalt nanoparticles forming were finished in one step. Scanning electron microscopy (SEM) images, transmission electron microscopy (TEM), energy-dispersive X-ray (EDS), X-ray photoelectron spectrometer (XPS) and X-ray diffraction (XRD) were applied to characterize the as-prepared CoNPs-N-GR. Moreover, owing to the presence of dopamine, high dispersed cobalt nanoparticles were obtained, leading to high electrocatalytic activity of CoNPs-N-GR for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline media. HER reaches 10 mA cm−2 at the over-potential of 0.453 V with a Tafel slope of 67 mV dec−1. OER reaches 10 mA cm−2 at the over-potential of 1.63 V with a Tafel slope of 65 mV dec−1. And the as-prepared CoNPs-N-GR shows excellent durability in the long-term stability for HER and OER.

FeNi Cubic Cage@N-Doped Carbon Coupled with N-Doped Graphene toward Efficient Electrochemical Water Oxidation

Oxygen evolution reaction (OER) is of great significance in electrochemical water splitting on industrial scale, which suffers from the slow kinetics and large overpotential, thus setting the main obstacle for efficient water electrolysis. To pursue cost-effective OER electrocatalysts with high activity and durable stability, we here set a facile strategy to prepare N-doped graphene supported core–shell FeNi alloy@N-doped carbon nanocages (FeNi@NC-NG) by annealing graphene oxides supported Prussian blue analogues under H2/Ar atmosphere. Based on the specific structural benefits, the present catalyst shows superior OER catalytic activity than precious metal catalyst of RuO2 and Ir/C, with a low overpotential of 270 mV for 10 mA cm–2, as well as high stability. The simple synthesis process and outstanding electrocatalytic performances show great potential of FeNi@NC-NG to replace the noble metal-based catalysts toward electrochemical water oxidation.

Bimetallic Ni–Fe phosphide nanocomposites with a controlled architecture and composition enabling highly efficient electrochemical water oxidation

A series of bimetallic Ni–Fe phosphide nanocomposites with a controlled architecture and composition are finely engineered for efficient electrocatalytic water oxidation.

A bioinspired soluble manganese cluster as a water oxidation electrocatalyst with low overpotential

The electrocatalytic oxidation of water is a challenging step towards the production of hydrogen as an alternative fuel. In nature, water oxidation is catalysed by a high oxidation state Mn4CaO x cluster. The corresponding industrial development of manganese catalysts for water oxidation is very attractive due to the low cost of this metal. A few manganese complexes have been previously explored as water oxidation catalysts using various chemical oxidants in homogeneous and heterogeneous systems. Efficient electrochemical water oxidation catalysed by a soluble manganese-oxo cluster, however, has not been achieved. Here, we report the synthesis and characterization of [Mn12O12(O2CC6H3(OH)2)16(H2O)4] (Mn12DH), a unique example within this class of compounds in being both highly soluble and stable in water. We demonstrate that Mn12DH, which is readily prepared from cheap and environmentally benign starting materials, is a stable homogeneous water oxidation electrocatalyst operating at pH 6 with an exceptionally low overpotential of only 334 mV. During photosynthesis, nature uses an enzyme with a manganese–calcium core for water oxidation. Here, the authors report the synthesis of a stable, water-soluble manganese cluster that acts as a homogeneous water oxidation electrocatalyst, displaying low overpotential and high Faradaic efficiency.

Rational Design of Cobalt-Iron Selenides for Highly Efficient Electrochemical Water Oxidation.

Exploring active, stable, earth-abundant, low-cost, and high-efficiency electrocatalysts is highly desired for large-scale industrial applications toward the low-carbon economy. In this study, we apply a versatile selenizing technology to synthesize Se-enriched Co1-xFexSe2 catalysts on nickel foams for oxygen evolution reactions (OERs) and disclose the relationship between the electronic structures of Co1-xFexSe2 (via regulating the atom ratio of Co/Fe) and their OER performance. Owing to the fact that the electron configuration of the Co1-xFexSe2 compounds can be tuned by the incorporated Fe species (electron transfer and lattice distortion), the catalytic activity can be adjusted according to the Co/Fe ratios in the catalyst. Moreover, the morphology of Co1-xFexSe2 is also verified to strongly depend on the Co/Fe ratios, and the thinner Co0.4Fe0.6Se2 nanosheets are obtained upon selenization treatment, in which it allows more active sites to be exposed to the electrolyte, in turn promoting the OER performance. The Co0.4Fe0.6Se2 nanosheets not only exhibit superior OER performance with a low overpotential of 217 mV at 10 mA cm-2 and a small Tafel slope of 41 mV dec-1 but also possess ultrahigh durability with a dinky degeneration of 4.4% even after 72 h fierce water oxidation test in alkaline solution, which outperforms the commercial RuO2 catalyst. As expected, the Co0.4Fe0.6Se2 nanosheets have shown great prospects for practical applications toward water oxidation.

Correction: Ni-based heterogeneous catalyst from a designed molecular precursor for the efficient electrochemical water oxidation.

Correction for 'Ni-based heterogeneous catalyst from a designed molecular precursor for the efficient electrochemical water oxidation' by Denis A. Kuznetsov et al., Chem. Commun., 2016, 52, 9255-9258.

Highly crystalline β-FeOOH(Cl) nanorod catalysts doped with transition metals for efficient water oxidation

Highly crystalline Ni-doped β-FeOOH(Cl) nanorod catalysts for efficient electrochemical water oxidation were successfully synthesized by a one-pot ambient temperature synthesis.

In situ formation of high performance Ni-phytate on Ni-foam for efficient electrochemical water oxidation

Electrochemical water splitting in an alkaline electrolyte for large-scale hydrogen production is currently a hot research topic. However, developing high-performance and durable oxygen-evolving electrocatalysts is an ongoing challenge. In this work we prepared Ni-phytate thin films with a bubble-like structure on Ni-foam through an in situ growth process. The resulting material can be used as an oxygen-evolving electrode in basic media without requiring the use of a conductive binder. The Ni-phytate electrode has high catalytic activity (ηj=10mAcm−2=280mV) and good stability (the current activity remained 95% after 5h) towards OER. This is an effective approach to simplifying the large-scale preparation of catalysts for water-splitting applications.

Carbon-Coated Co(3+)-Rich Cobalt Selenide Derived from ZIF-67 for Efficient Electrochemical Water Oxidation.

Oxygen evolution reaction (OER) electrocatalysts are confronted with challenges such as sluggish kinetics, low conductivity, and instability, restricting the development of water splitting. In this study, we report an efficient Co(3+)-rich cobalt selenide (Co0.85Se) nanoparticles coated with carbon shell as OER electrocatalyst, which are derived from zeolitic imidazolate framework (ZIF-67) precursor. It is proposed that the organic ligands in the ZIF-67 can effectively enrich and stabilize the Co(3+) ions in the inorganic-organic frameworks and subsequent carbon-coated nanoparticles. In alkaline media, the catalyst exhibits excellent OER performances, which are attributed to its abundant active sites, high conductivity, and superior kinetics.

Nickel-vanadium monolayer double hydroxide for efficient electrochemical water oxidation.

Highly active and low-cost electrocatalysts for water oxidation are required due to the demands on sustainable solar fuels; however, developing highly efficient catalysts to meet industrial requirements remains a challenge. Herein, we report a monolayer of nickel–vanadium-layered double hydroxide that shows a current density of 27 mA cm−2 (57 mA cm−2 after ohmic-drop correction) at an overpotential of 350 mV for water oxidation. Such performance is comparable to those of the best-performing nickel–iron-layered double hydroxides for water oxidation in alkaline media. Mechanistic studies indicate that the nickel–vanadium-layered double hydroxides can provide high intrinsic catalytic activity, mainly due to enhanced conductivity, facile electron transfer and abundant active sites. This work may expand the scope of cost-effective electrocatalysts for water splitting.