Interface Engineering of NixSy@MnOxHy Nanorods to Efficiently Enhance Overall-Water-Splitting Activity and Stability (original) (raw)
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ACS Omega
We report water-splitting application of chemically stable self-grown nickel sulfide (Ni x S y) electrocatalysts of different nanostructures including rods, flakes, buds, petals, etc., synthesized by a hydrothermal method on a threedimensional Ni foam (NiF) in the presence of different sulfurion precursors, e.g., thioacetamide, sodium thiosulfate, thiourea, and sodium sulfide. The S 2− ions are produced after decomposition from respective sulfur precursors, which, in general, react with oxidized Ni 2+ ions from the NiF at optimized temperatures and pressures, forming the Ni x S y superstructures. These Ni x S y electrocatalysts are initially screened for their structure, morphology, phase purity, porosity, and binding energy by means of various sophisticated instrumentation technologies. The as-obtained Ni x S y electrocatalyst from sodium thiosulfate endows an overpotential of 200 mV. The oxygen evolution overpotential results of Ni x S y electrocatalysts are comparable or superior to those reported previously for other self-grown Ni x S y superstructure morphologies.
Catalysis Letters, 2020
This review focusses on the recent developments in designing Layered Double Hydroxides (LDHs) with conductive, interlayer anion replacement, for efficient hydrogen fuel production by water splitting through Oxygen Evolution Reactions (OER) and Hydrogen Evolution Reactions (HER). Nickel nano structured catalysts improves OER performance are highlighted in detail in terms of compositional differences between transitional metal components, and challenges in future designing of rationalized Ni and Ni nano LDHs. The layered structure has exceptional flexibility of incorporating mixed valence transition metal ions into the LDHs structure in different compositions and this opens the massive potential to design high-performance LDHs catalysts on the molecular and nanometer scales. LDHs such as NiCoFe LDHs, Ni foam, Co Ni nano spheres, RuO 2 , Ir(dppe) 2 Cl, NiS 2 , Ni-N-Co-doped carbon nano fibers, NiCoSe 2 /cHRD are attracting increasing interest in the field of water splitting into hydrogen and oxygen due to their unique physicochemical properties. The highlighted summary will provide useful information in the development of novel Ni LDHs catalysts, which enables better understanding of OER properties valuable to address key issues. Increased fundamental understanding of water splitting catalysts would allow for rationallydirected improvements.
ACS Applied Materials & Interfaces
Large-scale H2 production from water by electrochemical water splitting is mainly limited by the sluggish kinetics of the non-precious based anode catalysts for oxygen evolution reaction (OER). Here, we report layer-by-layer in situ growth of low-level Fe-doped Ni-layered double hydroxide (Ni1-xFex-LDH), and Co-layered double hydroxide (Co1-xFex-LDH), respectively, with 3D microflower and 1D nanopaddy-like morphologies on Ni foam, by a one-step eco-friendly hydrothermal route. In this work, an interesting finding is that both Ni1-xFex-LDH and Co1-xFex-LDH materials are very active and efficient for OER as well as hydrogen evolution reaction (HER) catalytic activities in alkaline medium. The electrochemical studies demonstrate that Co1-xFex-LDH material exhibits very low OER and HER overpotentials of 249 and 273 mV, respectively at a high current density of 50 mA cm-2, while Ni1-xFex-LDH exhibits 297 and 319 mV. In order to study the overall water splitting performance using these electrocatalysts as anode and cathode, three types of alkaline electrolyzers are fabricated namely Co1-xFex-LDH(+)ǁCo1-xFex-LDH(-), Ni1-xFex-LDH(+)ǁNi1-xFex-LDH(-) and Co1-xFex-LDH(+)ǁNi1-xFex-LDH(-). These electrolyzers require only a cell potential (Ecell) of 1.60, 1.60 and 1.59 V, respectively, to drive the benchmark current density of 10 mA cm-2. Another interesting finding is that their catalytic activities are enhanced after stability tests. Systematic analyses are carried out on both the electrodes after all electrocatalytic activity studies. The developed three types of electrolyzers are very efficient to produce H2, cost-effective, offers no complications in synthesis of materials and fabrication of electrolyzers, which can greatly enable the realization of clean renewable energy infrastructure.
The design and fabrication of earth-abundant and highly efficient water oxidation electrocatalysts are important for water splitting systems associated with the energy conversion and storage. In this work, we report an intercalation strategy to expand interlayer spacing of the layered structure and thus achieve great enhancement for water oxidation activity. Layered-structured nickel benzoate hydroxide nanobelts arrays on nickel foam (benzoate-Ni(OH) 2 /NF) are prepared by a one-step hydrothermal method. As-prepared benzoate-Ni(OH) 2 /NF exhibits outstanding oxygen evolution performance with the need of only 242 mV overpotential to drive a current density of 60 mA cm −2 in 1.0 M KOH, 126 mV lower than that for Ni(OH) 2 / NF. This catalyst electrode also has good stability with the maintenance of its catalytic activity for 27 h. ■ INTRODUCTION Water electrolysis is currently acknowledged as an attractive approach for hydrogen production, which can well relieve the global energy crisis and environmental deterioration caused by increased depletion of fossil fuels. 1,2 However, electrocatalytic water splitting is seriously limited by the intrinsically sluggish kinetics of oxygen evolution reaction (OER) as the energy intensive step. 3,4 Hence, effective catalysts are demanded to accelerate the OER process and thus decrease the overpotential requirement. Ru and Ir oxides are the most active OER catalysts, but they suffer from scarcity, high cost, and instability during long-term electrolysis in alkaline medium, which hinders their large-scale applications. 5,6 Accordingly, extensive efforts have been devoted to the development of high-efficiency alternatives made from cost-effective materials. Layered metal hydroxides (LMHs) with brucite-like structures have emerged as promising earth-abundant materials with excellent electrochemical activity, 7−12 and various strategies have been proposed to further improve the electrochemical performance of LMHs. 13−17 Jin and co-workers reported layered α-cobalt hydroxide intercalated by large charge-balancing anions for the expansion of its interlayer spacing, and the larger interlayer distance allows for more accessible surface areas leading to enhanced capacitive performance. 17 Some work also demonstrates that LMHs with expanded interlayer spacing catalyze water oxidation more efficiently. 18−21 Additionally, previous reports have verified that more effective electrocatalysis can be achieved by directly growing catalyst nanoarrays on current collectors because of decreased series resistance, more exposed active sites, and facilitated diffusion of electrolytes. 22,23 Our recent work also indicates that benzoate anions are effective intercalators for layered cobalt hydroxide nanoarrays toward efficient OER electrocatalysis. 24 Given the Ni is more earth-abundant than Co, it is interesting to investigate the intercalation effect of benzoate anions on the OER activity of Ni-based LMHs nanoarrays, which, however, has not been explored before. In this work, we report layered nickel hydroxide intercalated by benzoate ions (0.7 nm in length) via a simple hydrothermal process to expand its interlayer spacing. Such benzoate-intercalated layered nickel hydroxide nanobelts arrays on nickel foam (benzoate-Ni(OH) 2 /NF) show greatly enhanced OER performance. Behaving as a 3D durable electrocatalyst for water oxidation in 1.0 M KOH, benzoate-Ni(OH) 2 /NF requires the overpotential of only 242 mV to afford 60 mA cm −2 , and much increased overpotential (368 mV) is demanded for Ni(OH) 2 / NF. Also, its catalytic activity can be maintained for at least 27 h.
Nanoscale nickel oxide/nickel heterostructures for active hydrogen evolution electrocatalysis
Nature Communications, 2014
Active, stable and cost-effective electrocatalysts are a key to water splitting for hydrogen production through electrolysis or photoelectrochemistry. Here we report nanoscale nickel oxide/nickel heterostructures formed on carbon nanotube sidewalls as highly effective electrocatalysts for hydrogen evolution reaction with activity similar to platinum. Partially reduced nickel interfaced with nickel oxide results from thermal decomposition of nickel hydroxide precursors bonded to carbon nanotube sidewalls. The metal ion-carbon nanotube interactions impede complete reduction and Ostwald ripening of nickel species into the less hydrogen evolution reaction active pure nickel phase. A water electrolyzer that achieves B20 mA cm À 2 at a voltage of 1.5 V, and which may be operated by a single-cell alkaline battery, is fabricated using cheap, non-precious metal-based electrocatalysts.
Nickel-based anodic electrocatalysts for fuel cells and water splitting
2016
Our world is facing an energy crisis, so people are trying to harvest and utilize energy more efficiently. One of the promising ways to harvest energy is via solar water splitting to convert solar energy to chemical energy stored in hydrogen. Another of the options to utilize energy more efficiently is to use fuel cells as power sources instead of combustion engines. Catalysts are needed to reduce the energy barriers of the reactions happening at the electrode surfaces of the water-splitting cells and fuel cells. Nickel-based catalysts happen to be important nonprecious electrocatalysts for both of the anodic reactions in alkaline media. In alcohol fuel cells, nickel-based catalysts catalyze alcohol oxidation. In water splitting cells, they catalyze water oxidation, i.e., oxygen evolution. The two reactions occur in a similar potential range when catalyzed by nickel-based catalysts. Higher output current density, lower oxidation potential, and complete substrate oxidation are preferred for the anode in the applications. In this dissertation, the catalytic properties of nickel-based electrocatalysts in alkaline medium for fuel oxidation and oxygen evolution are explored. By changing the nickel precursor solubility, nickel complex nanoparticles with tunable sizes on electrode surfaces were synthesized. Higher methanol oxidation current density is achieved with smaller nickel complex nanoparticles. DNA aggregates were used as a polymer scaffold to load nickel ion centers and thus can oxidize methanol completely at a potential about 0.1 V lower than simple nickel electrodes, and the methanol oxidation pathway is changed. Nickel-based catalysts also have electrocatalytic activity towards a wide range of substrates. Experiments show that methanol, ethanol, glycerol and glucose can be deeply oxidized and carbon-carbon bonds can be broken during the oxidation. However, when comparing methanol oxidation reaction to oxygen evolution reaction catalyzed by current nickel-based catalysts, methanol oxidation suffers from high overpotential and catalyst poisoning by high concentration of substrates, so current nickel-based catalysts are more suitable to be used as oxygen evolution catalysts. A photoanode design that applies nickel oxides to a semiconductor that is incorporated with surface-plasmonic metal electrodes to do solar water oxidation with visible light is proposed.
Advanced Materials, 2020
For example, Pt has been regarded as the best catalyst for hydrogen evolution reaction (HER), while IrO 2 and RuO 2 display excellent activities in oxygen evolution reaction (OER). [14,15] Unfortunately, the extensive usage toward the electrochemical energy conversion is impeded by their scarce and luxury nature. [16-18] Recently, it has been reported that nonprecious-metal nanomaterials can be used as the potential alternative catalysts for HER or OER. [19-27] For example, Ni-based sulfides and phosphides were synthesized for the electrocatalytic HER, [20,23] and Nibased oxides and hydroxides exhibited electrochemical oxygen evolution activities. [25-28] Since the overall water splitting is critical in the practical application, it is desired to develop bifunctional electrocatalysts. [29-31] Recently, several Ni-based nanomaterials have been prepared and exhibited bifunctional electrocatalytic activities in HER and OER. [24,32,33] However, the overall catalytic performance still needs further improvement, and the preparation of highly active bifunctional Ni-based nanomaterials for the electrolysis of water still remains as a big issue. Construction of well-defined heterostructured 2D materials is expected to be an effective way to prepare multifunctional catalysts, [3,10,11,34] since heterostructured materials have exhibited unique physicochemical properties. [11,35-38] Specifically, in the electrochemical energy conversion reaction, the heterostructures can tune the electronic structure of the catalyst and change the adsorption and desorption energies of intermediate on the catalyst surface during the catalytic process, leading to high catalytic performance. [39] For example, both MoS 2 /Ni 3 S 2 and MoS 2 /Co 9 S 8 /Ni 3 S 2 heterostructured nanomaterials show enhanced catalytic performance in overall water splitting as compared to the Ni 3 S 2 catalyst. [24,40-42] Moreover, the ultrathin 2D feature allows high-density active sites to be exposed on the surface of catalyst to enhance the catalytic activity. [3,34,43,44] Herein, we report a partial reduction strategy to prepare ultrathin Ni(0)-embedded Ni(OH) 2 heterostructured nanosheets, referred to as Ni/Ni(OH) 2 nanosheets, in which the metallic Ni(0) was reduced from the Ni(II) on the surface of Ni(OH) 2 nanosheets by sodium formate (HCOONa).
ACS Catalysis, 2017
The persistently increasing energy consumption and the low abundance of conventional fuels have raised serious concerns all over the world. Thus, the development of technology for clean energy production has become the major research priority worldwide. The globalization of advanced energy conversion technologies like rechargeable metal-air batteries, regenerated fuel cells, and water splitting devices has been majorly benefitted by the development of apposite catalytic materials that can proficiently carry out the pertinent electrochemical processes like oxygen reduction reaction (ORR), oxygen evolution reaction (OER), hydrogen evolution reaction (HER), and water hydrolysis. Despite a handful of superbly performing commercial catalysts, the high cost and low electrochemical stability of precursors have consistently discouraged their long term viability. As a promising substitute of conventional platinum, palladium, iridium, gold, silver, and ruthenium based catalysts, various transition metal (TM) ions (for example, Fe, Co, Mo, Ni, V, Cu, etc.) have been exploited to develop advanced electroactive materials to outperform the state-of-art catalytic properties. Among these TMs, nickel has emerged as one of the most hopeful constituent due to its exciting electronic properties and anticipated synergistic effect to dramatically alter surface properties of materials to favor electrocatalysis. This review article will broadly confer about recent reports on nickel-Page 1 of 74 ACS Paragon Plus Environment ACS Catalysis 2 based nano-architectured materials and their applications toward ORR, OER, HER, and whole water splitting. Based on these applications and properties of nickel derivatives, futuristic outlook of these materials have also been presented.
High-efficiency non-precious catalysts are important for hydrogen and oxygen evolution reactions (HER and OER). Practical water splitting needs not only intrinsically active catalyst materials but also the maximization of their electrocatalytic capability in a real electrolyzer. Here, we report for the first time a Ni/Ni 2 P inverse opal architecture fabricated by surface engineering. The superior HER properties are enabled by maximum active crystallographic plane exposure and vertical alignment of Ni 2 P nanosheets on nickel inverse opal. It requires an overpotential of only 73 mV to drive a HER current density of À20 mA cm À2. After doping with Fe, the resulting Fe:Ni/Ni 2 P inverse electrode shows excellent OER performance with a very low overpotential (285 mV) at a current density of 20 mA cm À2. An alkaline electrolyzer using the two 3D structured electrodes could split water at 20 mA cm À2 with a low voltage of $1.52 V for 100 h. The catalytic activity is even superior to that of the noble metal catalyst couple (IrO 2 –Pt/C). This work provides a surface engineered opal structure to maximize the electrocatalyst properties in the systems with coupled electron transfer and mass transport.