Co oxide nanostructures for electrocatalytic water-oxidation: effects of dimensionality and related properties

Abstract

A facile hydrothermal synthesis route was explored to obtain various nanostructures of Co oxide for applications in electrocatalytic water-splitting. The effect of reaction time and metal precursor ions on the morphology of synthesized nanostructures was studied in detail with the aid of a scanning electron microscope. By systematic optimization of the synthesis parameters, Co oxide nanostructures with single dimensionality were obtained in the form of 0D nanoparticles (NPs), 1D nanowires (NWs), 2D nanosheets (NSs) and 3D nanocrystals (NCs). The effectiveness of the developed nanostructures towards oxygen evolution reaction (OER) was studied and a promising OER activity was recorded for all the samples. Amongst all the developed catalysts, Co(OH)2 NPs showed the lowest overpotential of 339 mV to achieve a current density of 10 mA cm-2, which is even lower than that of noble-metal oxides such as the commercial RuO2 catalyst (370 mV). The specific effect of different parameters such as BET surface area, phase, crystallographic orientation of surface lattice planes, electroactive surface area and surface active species on the OER performance was studied. It was found that the Co3O4 phase is more active for the OER, compared to the Co(OH)2 phase. However, Co(OH)2 NPs showed the best OER performance owing to their higher BET surface area, thereby underlining the significance of the catalyst surface area. The effect of the number of active surface atoms was demonstrated by estimating the electroactive surface area of all Co3O4 nanostructures. It was also shown that the formation of CoO2 species (Co(IV)) on the surface is more beneficial for the OER as compared to the formation of CoOOH species (Co(III)). Finally, the robustness of the developed Co3O4 nanostructures was established by performing a recycling test for the OER (1000 cycles) and the observed change in the catalytic activity was correlated with morphological variation.

Alkaline Water Oxidation Using a Bimetallic Phospho‐Boride Electrocatalyst

“…The slope, obtained by linear fitting the plot of Δj (the difference in anodic and cathodic current densities at À 0.25 V) vs. scan rate, was employed to calculate the value of C DL . [54] Slow-scan CV with a scan rate of 2 mV s À 1 was performed in the pre-OER region to investigate the oxidation phenomenon on the catalyst surface. Faradaic efficiency (FE) tests were performed by measuring the evolved oxygen gas during a chronoamperometric test, using a bench-top NeoFox fluorometer coupled with a FOSPOR photoluminescence probe and purpose-built electrochemical cell.…”

Facile synthesis of Ni/NiO nanocomposites: the effect of Ni content in NiO upon the oxygen evolution reaction within alkaline media

“…In the search for NPM OER electrocatalysts, researchers have focused on a range of abundant and cheap oxides, such as nickel, iron, manganese and cobalt. [9][10][11][12][13][14][15] The OER is generally catalysed by a metal oxide rather than a pure metal, with the mechanism different for oxides with different surface morphologies. It has been reported that the OER activity of metal oxides follows the trend of NiO x > CoO x > FeO x > MnO x , 16,17 with Ni based oxides reported to exhibit the most promising OER catalysis owing to their high intrinsic activity; 18,19 In exemplifying the case of a metal surface versus a metal oxide, Babar et al 17 explored a thermally oxidized porous NiO supported on nickel foam (NF) in 1.0 M KOH towards the OER.…”

Research Progress on Non-noble Metal/Nitrogen-doped Carbon Composite Materials in Electrocatalytic Oxygen Evolution Reaction

“…过渡金属氧化物不仅储量丰富, 还具有特殊的 氧化还原性质以及良好的结构稳定性, 是一类常见 的电催化电极材料 [52][53][54] , 金属氧化物/碳氮复合材 料可以通过热解 MOF 的方式获得 [55] 。钴的氧化物 具有很好的 OER 催化活性, 然而纯氧化物较差的导 电性限制了材料的性能 [56][57] , 通过与氮掺杂碳材料 复合的方式可以有效改善材料导电性差的问题, 提高 其电催化性能。 Jin 等 [58] 通过一锅式热处理的方法制备 了一种钴-钴氧化物/氮掺杂碳复合材料(CoO x @CN), 金属钴和氧化钴、具有高导电性和大比表面积的碳 以及富电子氮的协同效应是材料具有高 OER 催化 活性(260 mV@10 mA•cm -2 )的主要原因。Li 等 [59] [59] ; (b, c)CoO 以及(d, e)N-CoO 纳米线阵列的 SEM 照片 [60] ; (f)CoO/Co@N-C 的 制备过程示意图 [61] ; (g)Co 3 O 4 微球, (h)葡糖糖包覆 Co 3 O 4 微球和(i)CoO/Co@N-C 的 SEM 照片 [61] ; (j)CoO@N-C、 CoO/Co@N-C、 盐酸刻蚀处理的 CoO/Co@N-C-x 样品组(x 表示刻蚀时间)、Ir/C 以及 Pt/C 在 0.1 mol•L -1 KOH 溶液中的(j)LSV 曲线和(k)Tafel 曲线 [61] ; (l)CoO/Co@N-C 催化剂在 0.1 mol•L -1 KOH 溶液中 2000 个 CV 循环前后的 LSV 曲线 [61] Fig. 5 (a) Illustration of the synthesis process of N-Co 3 O 4 and N-CoO/C [59] ; SEM images of (b, c) CoO and (d, e) N-CoO nanowire arrays [60] ; (f) Illustration of the synthesis process of CoO/Co@N-C [61] ; SEM images of (g) Co 3 O 4 and (h) Co 3 O 4 @Glu microspheres, and (i) CoO/Co@N-C electrocatalyst [61] ; (j) LSV curves and (k) Tafel plots of CoO@N-C, CoO/Co@N-C, CoO/Co@N-C-x samples that etched in HCl with x representing etching time, Ir/C and Pt/C in 0.1 mol•L -1 KOH solution; (l) LSV curves for the CoO/Co@N-C electrocatalyst before and after 2000 CV cycles in 0.1 mol•L -1 KOH solution [61] Colorful figures are available on website 表 4 非贵金属氧化物/碳氮复合材料 OER 催化性能比较表…”