Electrode For Overall Water Splitting Research Articles

Electrodeposited amorphous cobalt phosphosulfide on Ni foams for highly efficient overall water splitting

The surface self-reconstruction during the water splitting is considered as one key factor for the high catalytic activity. Owing to the exposure of more dangling bonds, amorphous structure is the ideal precursor to convert into the actual active phase in the process of electrocatalysis. Herein, amorphous cobalt phosphosulfide electrocatalysts are fabricated by a facile electrodeposition method on nickel foams as efficient bifunctional electrodes for overall water splitting. And benefited from the introduction of phosphorus and sulfur, the quantities of precursor sites are increased and the electronic state around cobalt is reconstructed, which provides more active phases and facilitates the transport efficiency of electrons. Electrochemical test results reveal that, the as-prepared cobalt phosphosulfide electrodes require overpotentials as low as 58 and 283 mV to achieve 10 mA cm−2 for hydrogen and oxygen evolution reactions in 1.0 M KOH, respectively. Tafel slopes and electrochemical impedance spectroscopy further illustrate a favorable kinetic during electrolysis. Meanwhile, it only requires a low cell voltage of 1.6 V for cobalt phosphosulfide electrodes to reach 10 mA cm−2 for overall water splitting.

Promotion of Overall Water Splitting Activity Over a Wide pH Range by Interfacial Electrical Effects of Metallic NiCo-nitrides Nanoparticle/NiCo2O4 Nanoflake/graphite Fibers.

Many efforts have been made to develop bifunctional electrocatalysts to facilitate overall water splitting. Here, a fibrous bifunctional 3D electrocatalyst is reported for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) with high performance. The remarkable electrochemical performance is attributed of the catalysts to a number of factors: the metallic character of the three components (i.e., Ni3N, CoN, and NiCo2O4); the electronic structure, nanoflake‐nanosphere network with abundant electroactive sites, and the electric field effect at the interfaces between different components. The oxide–nitride/graphite fibers have the lowest overpotential requirements of 71 and 183 mV at 10 mA cm−2 for HER and OER in alkaline medium, respectively. These values are comparable to those of commercial Pt/C (20 wt%) and RuO2. The electrodes also show a response to HER and OER in both neutral and acid media. Furthermore, the 3D structure can be highlighted by all‐round electrodes for overall water splitting. The calculations on the changes in electrons transfer and the Femi level from oxides to oxides/nitrides reveal that the observed superb electrocatalytic performance can be attributed to the presence of Ni3N and CoN derived from the in situ nitridation of NiCo2O4.

Controlled synthesis of 3D porous structured cobalt-iron based nanosheets by electrodeposition as asymmetric electrodes for ultra-efficient water splitting

Exploring more active, low-cost and stable electrocatalysts to substitute precious noble metals has always been a research focus on the application of water splitting. In this study, firstly, we prepared CoFe-layered double hydroxide (CoFe-LDH) via one-step electrodeposition. The CoFe-LDH nanosheets grew on the nickel foam and formed a 3D hierarchical structure, making the CoFe-LDH exhibit excellent activity for oxygen evolution reaction (OER). The overpotential was 250 mV and the Tafel slope is 35 mV dec−1 at 10 mA cm−2 in alkaline condition. With such a 3D porous structure as a framework, we fabricated CoFe phosphides using a solid-phase reaction. After phosphorization, the nanosheets retained the original 3D porous structure and electrochemical performance for hydrogen evolution reaction had been greatly enhanced. The overpotential in alkaline condition was 58 mV and the Tafel slope is 46 mV dec−1 at 10 mA cm−2. The CoFe-LDH and CoFe-P with Ni foams were used as asymmetric electrodes for overall water splitting. At the potential of 1.51 V, this electrolysis apparatus can reach a current density of 10 mA cm−2 in 1 M KOH, which is superior to all of the reported non-precious metal based ones.

Homogeneous core–shell NiCo2S4 nanorods as flexible electrode for overall water splitting

Exploring low-cost and highly efficient Water splitting electrocatalyst has been recognized as one of the most challenging and promising ways. NiCo2S4 core-shell nanorods supported on nickel foam (NF) have been fabricated by a facile hydrothermal method. The electrochemical performance of NiCo2S4@NiCo2S4 for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is studied. NiCo2S4@NiCo2S4/NF exhibits a significantly improved OER and HER performance with an overpotential of 200 mV at 40 mA/cm2 and an overpotential of 190 mV at 10 mA/cm2. The combination of low charge-transfer resistance, enhanced interaction and charge transport as well as large electrochemical double-layer capacitance enables superior OER and HER. The NiCo2S4@NiCo2S4/NF nanorod electrode shows excellent electrocatalytic activity with a low voltage 1.57 V and stability with long hour electrolysis, which is highly satisfactory for a prospective bifunctional electrocatalyst.

In situ formation of consubstantial NiCo2S4 nanorod arrays toward self-standing electrode for high activity supercapacitors and overall water splitting

Developing high-efficiency, low-cost and environmental friendly electrode materials for both supercapacitors and overall water splitting are significant for renewable energy storage and conversion. Herein, we report a facile consubstantial growth strategy to fabricate subuliform NiCo2S4 nanorod arrays electrode through an in situ growing process, utilizing self-sacrificial Ni foam as substrate and Ni resource. Benefitting from the unique structures, the subuliform NiCo2S4 nanorods can be directly serve as binder-free, trifunctional electrode for overall water splitting with excellent electrocatalytic activity (oxygen evolution reaction with low overpotential of 220 mV at 30 mA cm−2 and hydrogen evolution reaction with low overpotential of 222 mV at 30 mA cm−2) and also as a promising pseudocapacitance electrode with superior electrochemical performance and good stability (high areal capacitance of 8.85 F cm−2 at a current density of 10 mA cm−2 and 94.96% capacitive retention after 10000 cycles). The present work highlights the remarkable advantages of the self-sacrificial strategy for the design of high-performance multifunctional electrode materials.

Electrocatalysis: Ultrafine Pt Nanoparticle‐Decorated Pyrite‐Type CoS2 Nanosheet Arrays Coated on Carbon Cloth as a Bifunctional Electrode for Overall Water Splitting (Adv. Energy Mater. 24/2018)

In article number 1800935, Cheng Zhong, Wenbin Hu, and co-workers report ultrafine Pt nanoparticles decorated CoS2 nanosheet arrays coated on carbon cloth as a bifunctional electrode for overall water-splitting. The integrated composite exhibits superior electrochemical performance owing to the interfacial and electronic synergy between Pt and CoS2, which optimizes the hydrogen adsorption/desorption behaviors and facilitates the in situ generation of active species.

Strong Electronic Interaction in Dual-Cation-Incorporated NiSe2 Nanosheets with Lattice Distortion for Highly Efficient Overall Water Splitting.

Exploring highly efficient and low-cost electrocatalysts for electrochemical water splitting is of importance for the conversion of intermediate energy. Herein, the synthesis of dual-cation (Fe, Co)-incorporated NiSe2 nanosheets (Fe, Co-NiSe2 ) and systematical investigation of their electrocatalytic performance for water splitting as a function of the composition are reported. The dual-cation incorporation can distort the lattice and induce stronger electronic interaction, leading to increased active site exposure and optimized adsorption energy of reaction intermediates compared to single-cation-doped or pure NiSe2 . As a result, the obtained Fe0.09 Co0.13 -NiSe2 porous nanosheet electrode shows an optimized catalytic activity with a low overpotential of 251 mV for oxygen evolution reaction and 92 mV for hydrogen evolution reaction (both at 10 mA cm-2 in 1 m KOH). When used as bifunctional electrodes for overall water splitting, the current density of 10 mA cm-2 is achieved at a low cell voltage of 1.52 V. This work highlights the importance of dual-cation doping in enhancing the electrocatalyst performance of transition metal dichalcogenides.

Water Splitting Catalysts: Colloidal Synthesis of Mo–Ni Alloy Nanoparticles as Bifunctional Electrocatalysts for Efficient Overall Water Splitting (Adv. Mater. Interfaces 13/2018)

Colloidal synthesis of highly monodispersed Mo–Ni alloy nanoparticles is achieved by thermal decomposition of by thermal decomposition of Ni(acac)2 and Mo(CO)6 in the presence of 1-octadecene and oleyamine at 320 °C. The optimal Mo0.6Ni0.4 alloy nanoparticles exhibit excellent performance for both the water splitting reactions, namely, hydrogen evolution reaction and oxygen evolution reaction. This attribute of the as-prepared alloy nanoparticles allows one to construct a two-electrode electrolyzer by using them as bifunctional catalysts. An added benefit here is the ease of depositing them on on-demand substrates to fabricate either rigid or flexible high-performance electrodes for overall water splitting. More details can be found in article 1800359 by Taotao Zhang, Xiaowang Liu, Baoyou Geng and co-workers.

Controlled Synthesis of a Three-Segment Heterostructure for High-Performance Overall Water Splitting.

Developing earth-abundant, highly active, and robust electrocatalysts capable of both oxygen and hydrogen evolution reactions is crucial for the commercial success of renewable energy technologies. Here we demonstrate a facile and universal strategy for fabricating transition metal (TM) sulfides by controlling the atomic ratio of TM precursors for water splitting in basic media. Density functional theory calculations reveal that the incorporation of Fe/Co can significantly improve the catalytic performance. The optimal material exhibits extremely small overpotentials of 208 mV for oxygen evolution and 68 mV for hydrogen evolution at 10 mA cm-2 with robust long-term stability. The optimized material was used as bifunctional electrodes for overall water splitting, which delivers 10 mA cm-2 at a very low cell voltage of 1.44 V with robust stability over 80 h at 100 mA cm-2 without degradation, much better than the combination of Pt and RuO2 as benchmark catalysts. The excellent water-splitting performance sheds light on the promising potential of such sulfides as high activity and robust stable electrodes.

Ultrafast fabrication of nickel sulfide film on Ni foam for efficient overall water splitting.

Development of low-cost, high performance and stable non-noble electrocatalysts with both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) activities for overall water splitting is essential for future energy supply. Herein, for the first time, a facile and ultrafast synthetic method has been reported to fabricate nickel sulfide (Ni3S2) films on Ni foam (Ni3S2/NF) as efficient bifunctional electrodes for overall water splitting through direct dropping of mercaptoethanol solution followed by annealing at 300 °C for only 50 s. Thanks to the integrated three-dimensional (3D) configuration, the obtained Ni3S2/Ni foam exhibits excellent activity and stability for HER and OER with low overpotentials of 131 and 312 mV, respectively, to attain a current density of 10 mA cm-2 in alkaline media. Ni(OH)x species formed on the Ni3S2 surface serves as the actual catalytic site during OER reaction. Given the well-defined bifunctionality, an overall water-splitting device using two identical Ni3S2/NF electrodes delivers a current density of 10 mA cm-2 at a low cell voltage of 1.68 V in an alkaline water electrolyzer. This approach is promising as a simple method for depositing a wide range of useful transition metal sulfide electrocatalysts on corresponding metal substrate bifunctional electrodes for overall water splitting, shedding some light on the development of functional materials in energy chemistry.

Tunable 3D hierarchical Ni3S2superstructures as efficient and stable bifunctional electrocatalysts for both H2and O2generation

3D hierarchical Ni3S2superstructures arein situgrown on nickel foam to build self-supported electrode for overall water splitting.

3D cellular CoS1.097/nitrogen doped graphene foam: a durable and self-supported bifunctional electrode for overall water splitting

3D cellular N-doped graphene foam supported CoS1.097 nanoparticles as highly active and stable bifunctional catalysts for overall water splitting.

Highly active and dual-function self-supported multiphase NiS–NiS2–Ni3S2/NF electrodes for overall water splitting

A bifunctional self-supported electrode for water splitting to achieve a dynamic balance between HER and OER constructed via a one-step direct thermal sulfidization of NF.

Template-free synthesis of coral-like nitrogen-doped carbon dots/Ni3S2/Ni foam composites as highly efficient electrodes for water splitting

Non-noble, high-efficient electrodes with excellent durability are desirable for water splitting. Herein, a facile strategy has been proposed to in-situ grow nitrogen-doped carbon dots (NCDs) decorated Ni3S2 on Ni foam (NCDs/Ni3S2/NF) by hydrothermal treatment of Ni foam in water solution of thiourea and NCDs. Interestingly, coral-like NCDs/Ni3S2/NF composites are unprecedentedly prepared without any templates, where the Ni3S2 nanorods mainly expose {021} high-index facets. The resultant NCDs/Ni3S2/NF composites are directly used as self-supported electrodes for overall water splitting which deliver a current density of 10 mA cm−2 at 1.50 V with excellent durability in 1.0 M KOH solution.

Facile synthesis of free-standing nickel chalcogenide electrodes for overall water splitting

Developing high-performance noble metal-free and free-standing catalytic electrodes are crucial for overall water splitting. Here, nickel sulfide (Ni3S2) and nickel selenide (NiSe) are synthesized on nickel foam (NF) with a one-pot solvothermal method and directly used as free-standing electrodes for efficiently catalyzing hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline solution. In virtue of abundant active sites, the Ni3S2/NF and the NiSe/NF electrodes can deliver a current density of 10 mA cm−2 at only 123 mV, 137 mV for HER and 222 mV, 271 mV for OER. Both of the hierarchical Ni3S2/NF and NiSe/NF electrodes can serve as anodes and cathodes in electrocatalytic overall water-splitting and can achieve a current density of 10 mA cm−2 with an applied voltage of ∼1.59 V and 1.69 V, respectively. The performance of as-obtained Ni3S2/NF||Ni3S2/NF is even close to that of the noble metal-based Pt/C/NF||IrO2/NF system.

Acid promoted Ni/NiO monolithic electrode for overall water splitting in alkaline medium

Exploring and designing bi-functional catalysts with earth-abundant elements that can work well for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline medium are of significance for producing clean fuel to relieve energy and environment crisis. Here, a novel Ni/NiO monolithic electrode was developed by a facile and cost-effective acid promoted activation of Ni foam. After the treatment, this obtained monolithic electrode with a layer of NiO on its surface demonstrates rough and sheet-like morphology, which not only possesses larger accessible surface area but also provides more reactive active sites. Compared with powder catalysts, this monolithic electrode can achieve intimate contact between the electrocatalyst and the current collector, which will alleviate the problem of pulverization and enable the stable function of the electrode. It can be served as an efficient bi-functional electrocatalyst with an overpotential of 160 mV for HER and 290 mV for OER to produce current densities of 10 mA cm−2 in the alkaline medium. And it maintains benign stability after 5,000 cycles, which rivals many recent reported noble-metal free catalysts in 1.0 mol L−1 KOH solution. Attributed to the easy, scalable methodology and high catalytic efficiency, this work not only offers a promising monolithic catalyst but also inspires us to exploit other inexpensive, highly efficient and self-standing noble metalfree electrocatalysts for scale-up electrochemical water-splitting technology.

Cobalt disulfide/graphite foam composite films as self-standing electrocatalytic electrodes for overall water splitting.

The development of ecofriendly electrocatalysts with earth-abundant metal elements for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is important for overall water splitting to generate clean and sustainable chemical energy. Here, we report a self-standing cobalt disulfide/graphite foam (CoS2/GF) electrocatalytic electrode for this purpose. It showed high catalytic activities for both the HER and OER, requiring only a cell voltage of 1.74 V to achieve a current density of 20 mA cm-2 for overall water splitting in an alkaline electrolyte. This three-dimensional microporous electrocatalytic electrode is cheap and available in a large area; thus, it is attractive for practical applications.

Direct growth of cobalt-rich cobalt phosphide catalysts on cobalt foil: an efficient and self-supported bifunctional electrode for overall water splitting in alkaline media

Cobalt-rich cobalt phosphide catalysts on cobalt foils as integrated bifunctional electrodes have been developed and display outstanding performances towards overall water splitting.

Vertically oriented cobalt selenide/NiFe layered-double-hydroxide nanosheets supported on exfoliated graphene foil: an efficient 3D electrode for overall water splitting

A 3D ternary hybrid containing Co0.85Se nanosheet-array and NiFe-LDH grown on electrochemically exfoliated graphene was synthesized for highly-efficient overall water-splitting.’

Self-supported NiMo hollow nanorod array: an efficient 3D bifunctional catalytic electrode for overall water splitting

A NiMo hollow nanorod array is developed on Ti mesh via a template-assisted electrodeposition method as a bifunctional electrode for water splitting.