Promoting the Water Oxidation Catalysis by Synergistic Interactions between Ni(OH)₂ and Carbon Nanotubes

Abstract

capsulating the electrocatalysts. [27,[43][44][45][46] Recently, Zhao and coworkers [47] and Dai and co-workers [48,49] anchored Co, Ni-Fe based water splitting catalysts on multiwall carbon nanotubes (MWCNTs), these approaches not only enhanced the charge transportations but also increased the available catalytic sites. Although the obtained materials exhibit excellent activity toward water oxidation, the improvement are not significant compared to the original catalysts. Very recently, Zhao and co-workers [50] reported a metal free catalyst based on oxidized MWCNTs (O-MWCNTs) which shows comparable activities to the transition metal-based catalysts, due to the generated oxygen containing ketone groups on surface. This work inspired us to revisit the inorganic/nanocarbon hybrid materials in pursuit of more advanced OER electrocatalysts.As desired, a surprisingly high active OER catalyst has been obtained by simply anchoring the crystalline β−Ni(OH) 2 onto the O-MWCNTs. Different from previous studies, this is the first time that a hybrid material with low Ni contents exhibits extremely high activities for catalyzing oxygen evolution. [41,46] This work paves the path for designing new earth abundant material based alternatives to replace the benchmarking precious Ir/Ru OER catalysts.In order to densely embed the Nickel hydroxide on the MWCNT S , a two-step synthetic strategy was employed to synthesize the hybrid materials as shown in Figure 1. First, the as purchased MWCNTs were purified and mildly oxidized by a piranha solution followed by hydrothermal treatment according to the literature method. [50] Afterward, the freshly obtained O-MWCNTs were mixed with the hydrolysed Ni 2+ solution to afford the hybrid materials. NH 4 OH was introduced as the precipitating reactant instead of strong alkali solution to obtain a particularly pure nickel hydroxide. [51] To gain insights into how the Ni contents in the hybrid materials affect the efficiency toward catalytic water oxidation, five samples with various Ni contents were prepared following the same synthetic route (see the Supporting Information).To gain insight into the structure, morphologies, and composition of the synthesized materials, powder X-ray diffraction (PXRD), scanning electron microscopy, transmission electron microscopy (TEM), hard X-ray photoelectron spectroscopy measurements (HAXPES) and, thermogravimetry (TG) techniques were used to characterize these materials. The morphology of the O-MWCNTs was determined by TEM, as shown in Figure S2a in the Supporting Information. After the loading of Ni, PXRD, and HAXPES (Figure 2a and Figure 3) show that the obtained catalysts are composed of pure crystalline β-Ni(OH) 2 and O-MWCNTs, moreover, no metal impurities such as Fe and Co were detected ( Figure S1, SupportingThe rapid growth in energy demand, the continuous consumption of fossil fuels and the arising environmental concerns are stimulating significant research interests in developing alternative energy systems. [1] Production of hydrogen from electro...

Vertically Aligned Porous Nickel(II) Hydroxide Nanosheets Supported on Carbon Paper with Long‐Term Oxygen Evolution Performance

“…Therefore, all subsequente lectrocatalytic tests were only focused on the optimal CP@Ni(OH) 2 electrode. After preactivation, the CP@Ni(OH) 2 electrode only needs overpotentials of 1.54 (h 10 = 308 mV) and 1.57 V( h 20 = 338 mV) to attain current densities of 10 and 20 mA cm À2 ,r espectively;t hese values compare favorably to those of otherN i-based OER catalysts recently reported in the literature, such as a-Ni(OH) 2 hollow spheres (h 10 = 331 mV), [34] b-Ni(OH) 2 nanoplates (h 10 = 444 mV), [34] b-Ni(OH) 2 nanoparticles (h 10 = 340 mV), [36] b-Ni(OH) 2 porousn ano-plates (h 10 = 360 mV), [29] NiFe 2 O 4 /a-Ni(OH) 2 compounds (h 10 = 340 mV), [43] Ni 2 Pn anowires (h 10 = 400 mV), [30] and electrodeposited Ni-P thin films (h 10 = 344 mV), [31] although they are not as good as those of b-Ni(OH) 2 /O-MWCNT hybrids (h 10 = 270 mV) [37] and Ni-P porousnanoplates (h 10 = 300 mV) [29] (Table S2). For comparison, the OER activities of bare CP andC P/RuO 2 electrodes were also measured.…”

“…In this context, considerable research efforts have recently been de-voted to the search for efficient and inexpensive OER catalysts comprising earth-abundant elements, including transitionmetal oxides, [8][9][10] hydroxides, [11][12][13] perovskites, [14,15] phosphates, [16,17] sulfides, [18,19] and recently reported phosphides. [33][34][35][36][37][38][39][40] For example, Stern and Hu compared the OER performance of bulk Ni(OH) 2 films to that of Ni(OH) 2 nanoparticles and found that the Ni(OH) 2 nanoparticles only neededasmall overpotential (h)o f3 00 mV to deliver ac urrent density of 10 mA cm À2 (h 10 ), and thus, they substantially outperformed bulk Ni(OH) 2 films and demonstratedt he benefito fn anostructuring. Previous work on the OER performance of Ni(OH) 2 was primarily focusedo ne lectrodepositeda nd physically depositedt hin films.…”

“…[33][34][35][36][37][38][39][40] For example, Stern and Hu compared the OER performance of bulk Ni(OH) 2 films to that of Ni(OH) 2 nanoparticles and found that the Ni(OH) 2 nanoparticles only neededasmall overpotential (h)o f3 00 mV to deliver ac urrent density of 10 mA cm À2 (h 10 ), and thus, they substantially outperformed bulk Ni(OH) 2 films and demonstratedt he benefito fn anostructuring. [37] The excellent OER activity was ascribed to as ynergistic effect between Ni(OH) 2 and the MWCNTsa sw ell as the presence of oxygencontaining groups (e.g.,k etone and carboxylate) on the MWCNTst hat facilitated protont ransfer during the OER. [34] Although nanostructured Ni(OH) 2 is able to provide ag reater surfacea rea and more electrocatalytically active sites to allow for easy access to the electrolyte, the intrinsic electrical conductivity of Ni(OH) 2 is very poor such that fast charge transfer is difficult to achieve.…”

“…[34] Although nanostructured Ni(OH) 2 is able to provide ag reater surfacea rea and more electrocatalytically active sites to allow for easy access to the electrolyte, the intrinsic electrical conductivity of Ni(OH) 2 is very poor such that fast charge transfer is difficult to achieve. [33,34,37,39] Moreover,m ost Ni(OH) 2 nanostructures reported for use as OER catalysts were produced in the form of powders, [33][34][35][36][37]39] and Ni(OH) 2 nanostructures directly grown on current collectors have been rarely explored. [37] The excellent OER activity was ascribed to as ynergistic effect between Ni(OH) 2 and the MWCNTsa sw ell as the presence of oxygencontaining groups (e.g.,k etone and carboxylate) on the MWCNTst hat facilitated protont ransfer during the OER.…”

Highly Active Three‐Dimensional NiFe/Cu2O Nanowires/Cu Foam Electrode for Water Oxidation

“…First, linear sweep voltammetry (LSV) was conducted to test the electrochemical behavior of the NiFe/Cu 2 O NWs/CF electrode in 1.0 m KOH, as shown in Figure 6a . [31] Cyclic voltammograms of the non-faradaic region were recorded at various scan rates, and the C dl and ECSA of the NiFe/Cu 2 ON Ws/CF electrode were calculated to be 98 mF cm À2 and 2450 cm 2 ,r espectively.S uch al arge ECSA is of great help for enhancing the catalytic activity for the OER. In contrast, the OER did not proceed with the Cu 2 ON Ws/CF electrode until the oxidation potentialw as increased to 1.55 V versusR HE (black line).…”