Ni Inverse Opals for Water Electrolysis in an Alkaline Electrolyte

Yi, Huang; Lai, Chun‐Han; Wu, Pu Wei; Chen, Li Yin

doi:10.1149/1.3281332

Cited by 42 publications

(30 citation statements)

References 32 publications

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“…Recently, we have reported the fabrication of large-area colloidal crystals and their inverse opals at controlled thickness by electrophoresis and electrodeposition. 37,38 In particular, we demonstrate the formation of ZnO inverse opals with uniform surface morphology and reduced crystallographic defects. 39 In this work, we prepare the ZnO inverse opals in both semi-layered and multi-layered thickness and evaluate their respective EWOD behaviors.…”

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confidence: 78%

Electrowetting of Superhydrophobic ZnO Inverse Opals

Chen

Lai

et al. 2011

J. Electrochem. Soc.

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ZnO inverse opals are fabricated by electrophoresis of polystyrene (PS) microspheres (720 nm in diameter) on a ITO glass to form a close-packed colloidal crystal, followed by potentiostatic deposition of ZnO in the interstitial voids among the PS microspheres and chemical removal of the PS colloidal template. By adjusting the electrodeposition time, we obtain semi-layered and multilayered ZnO inverse structures with significantly reduced defects and considerable surface uniformity. The semi-layered ZnO inverse opals display a bowl-like morphology with individual cavities isolated from each other. In contrast, the multi-layered ZnO inverse opals exhibit a three-dimensional skeleton with hexagonally-arranged cavities interconnected to each other. After surface coating of perfluorodecyltriethoxysilane, both samples reveal a superhydrophobic nature with contact angle larger than 150. In electrowetting measurements, the contact angles are decreasing with increasing applied voltages. The droplet on the semi-layered ZnO inverse opals demonstrates a notable transition from the Cassie-Baxter state to the Wenzel one. However, the droplet on the multi-layered ZnO inverse opals indicates three distinct regimes; Cassie-Baxter state, mixed Cassie-Baxter/Wenzel state, and Wenzel state. Repelling pressure of the entrapped air in the cavities is estimated to explain the observed contact angle variation upon the applied voltage for both samples. The surface property for a solid material can be deliberately controlled from hydrophilic to hydrophobic in order to affect the wetting behavior of a water droplet that is in contact with the solid surface. So far, external stimuli such as electric field, mechanical force, magnetic field, electrochemical reaction, and photon excitation have been employed to manipulate physical and chemical attributes of the surface.1-5 Among them, the electrical route, known as electrowetting (EW), is recognized for its fast response, reversibility, and compatibility with microdevices.6-8 To date, the implementation of EW for applications such as microfluidics and optoelectronic components have been explored. [9][10][11] In EW, the water droplet on the solid surface reveals a significant morphological alteration from a large contact angle (hydrophobic) to a reduced one (hydrophilic) upon the imposition of voltage across the solid surface and water droplet. This is because the electrical field engenders a capacitive charging on the interface that increases its surface energy considerably. As a result, the water droplet is able to wet the solid surface lowering the overall interfacial energy.For a desirable EW material, a large contact angle at zero voltage and a stronger capacitive effect are always preferred. To achieve these objectives, recent research attention has focused on the design and fabrication of one-dimensional materials such as nanowires and nanorods. [12][13][14][15] In general, the wetting behavior for the water droplet on a nanostructured surface can be categorized in Cassie-Baxter model o...

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confidence: 78%

Electrowetting of Superhydrophobic ZnO Inverse Opals

Chen

Lai

et al. 2011

J. Electrochem. Soc.

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“…In our earlier studies of Ni inverse opals, we realized that the crystallinity of the colloidal template was critical for subsequent electroplating as it affected the percolation distance for the plating electrolyte that determined the iR E loss (R E is the electrolyte resistance) and uniformity of the Ni deposit. 19,36 This effect is expected to become more pronounced as the ZnO is insulative in nature so both the electrolyte and electrode resistance are varied for the entire plating process. In our observations, the PS template fell apart when it did not possess sufficient thickness.…”

Section: Resultsmentioning

confidence: 99%

Facile Electrochemical Fabrication of Large-Area ZnO Inverse Opals with Reduced Defects

Liao

Huang

et al. 2011

J. Electrochem. Soc.

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We demonstrate a facile fabrication scheme to construct large-area ZnO inverse opals on an indium-tin-oxide substrate with significantly reduced defects and improved stoichiometry. The fabrication steps involve the preparation of colloidal template via vertical electrophoresis of polystyrene (PS) microspheres in 720 nm radius, followed by galvanostatic electrodeposition of ZnO in the interstitial voids among the PS microspheres. Subsequently, the sample undergoes a heat-treatment in air at 500 C for different time to remove the colloidal template, leaving an integral ZnO skeleton with thickness adjusted by the electrodeposition time. Since the colloidal template is deliberately designed with desirable thickness and considerable uniformity, the electroplating of ZnO can be achieved in a reduced ethanol/water ratio that allows faster growth rate and improved ZnO structure. Scanning electron microscope images demonstrate negligible microstructural defects for the ZnO inverse opals. X-ray diffraction reveals a wurtzite hexagonal lattice with (002) preferred orientation. In addition, both X-ray photoelectron spectroscopy and photoluminescence spectra suggest improved crystallinity and stoichiometry with increasing heat-treatment time.

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“…Important factors to consider when choosing an electrocatalyst include its stability, performance, and cost. Many researchers have investigated nickel oxides as the electrocatalyst for the anodic oxygen evolution reaction [1][2][3][4][5][6][7], as it is much less costly than options such as iridium or ruthenium oxide and has reasonably good performance, with a potentials of approximately 750 mV vs. HgHgO at a current density of 50 mA cm -2 [8], and Tafel slopes as low as 38 mV. However, the performance stability under anodic conditions can be an issue, resulting in the performance of the electrocatalyst decreasing over time [6,8] As the loss in performance of nickel oxide anodes is generally accepted to be related to structural changes in the oxide, much of the research into nickel oxide electrocatalysts has involved investigating the structure of the electrocatalyst [6,[9][10][11][12].…”

Section: Introductionmentioning

confidence: 99%

Electrocatalytic oxygen evolution on nickel oxy-hydroxide anodes: Improvement through rejuvenation

Mellsop

Gardiner

Marshall

2015

Electrochimica Acta

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The ageing and rejuvenation behaviour of nickel oxy-hydroxide anodes for alkaline water electrolysis is investigated. The anodically formed oxy-hydroxide material is known to age over time causing a decrease in performance. However, this deactivation can be mitigated by temporarily reducing the potential for brief periods. This work looks at continuous rejuvenation of nickel anodes in 30wt.% KOH solution and it is shown that rejuvenation at 0.5 V vs. HgHgO for 10 minutes every 100 minutes can prevent ageing of the anode, thus maintaining a low overpotential during galvanostatic oxygen evolution at 50 mA cm -2 . It is suggested that the short potentiostatic rejuvenation periods at regular intervals prevents the ratio of Ni(IV) to Ni(III) from increasing, thereby maintaining the intrinsic activity of the material. The rejuvenation potential must be above 0.36 V vs. HgHgO to ensure it is effective in obtaining good performance (i.e. the material must not reduce to Ni(II)). These findings suggest that electrolysis systems using nickel anodes could benefit from direct coupling to fluctuating power sources such as solar or wind, where the variability in their power output could facilitate the rejuvenation of the nickel anode. We estimate that by using the rejuvenation steps, an energy saving of 9% is possible in an alkaline water electrolyser using nickel anodes.

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Ni Inverse Opals for Water Electrolysis in an Alkaline Electrolyte

Cited by 42 publications

References 32 publications

Electrowetting of Superhydrophobic ZnO Inverse Opals

Electrowetting of Superhydrophobic ZnO Inverse Opals

Facile Electrochemical Fabrication of Large-Area ZnO Inverse Opals with Reduced Defects

Electrocatalytic oxygen evolution on nickel oxy-hydroxide anodes: Improvement through rejuvenation

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