A facile method for preparing amorphous Co-Ni-Cu ternary hydroxides as an efficient oxygen evolution reaction electrocatalyst
Graphical abstract
Introduction
Electrocatalytic water splitting is limited by the bottleneck step of oxygen evolution reaction (OER) due to lack of high-efficient, low cost and stable catalysts. Although precious metal-based electrocatalysts had high catalytic activities, the poor long-term stability and high cost limit their large-scale industrial application [1]. Non-precious transition metal materials, such as sulfides, selenides, phosphides [2], etc., were developed as OER catalysts, however, their long-time catalytic stability were also unsatisfactory, because they would be oxidized to corresponding metal oxides or (oxo)hydroxides during catalytic processes. Therefore, transition metal based oxides and (oxo)hydroxides have been considered as the most promising OER electrocatalysts due to their excellent stability and high efficient [3]. In particular, nickel hydroxide has exhibited good catalytic performance for OER in alkaline media, and the doping with other transition metals like Fe, Cu, Co, etc. to form binary hydroxides or ternary hydroxides could further enhance its intrinsic catalytic activity [4]. Recently, several researches demonstrated that the ternary hydroxides have better catalytic performance than the corresponding binary hydroxides [5]. Furthermore, the charge-transfer effects of Co facilitated the oxidation of insulating Ni(OH)2 to conductive NiOOH [6], Cu could significantly improve the electrical conductivity of amorphous catalyst [7], which inspired us to design and prepare a ternary OER electrocatalyst and nickel hydroxide doped with Co and Cu was envisaged. In addition, amorphous structure was more favorable for OER than the crystalline ones, because it possessed a large number of structure defects and exposed more naked or unsaturated metal active sites, which facilitated the diffusion and reaction of electrolyte ions [8]. Therefore, in this work, we first prepared amorphous Co-Ni-Cu hydroxide via a simple co-precipitation method. The morphology, structure, and surface electronic states of the as-fabricated sample were investigated.
Section snippets
Synthesis of Co-Ni-Cu hydroxides
Typically, 2 mM Co(NO3)2·6H2O, 0.75 mM NiSO4·6H2O, 1.25 mM CuCl2·2H2O, 2 mM citric acid (C6H8O7·H2O) and 0.25 g polyvinyl pyrrolidone were dissolved in 10 mL deionized water under stirring. Then, 1.0 M KOH solution was slowly dropped into above solution under magnetic agitation until the solution pH being 8.5, and the mixture solution turned into grey-blue slurry. After centrifuged rinsed with deionized water and anhydrous ethanol for several times, the sample was dried at 60 ℃ for 12 h, and
Results and discussion
The morphology and structure of the dried CNC835 (actual molar ratio of Co:Ni:Cu is 6.2:3.1:5.0 according to ICPMS) was investigated by SEM (Fig. 1(a) and (b)) and TEM (Fig. 1(c)). Fig. 1(a) revealed that CNC835 was large blocks formed by stacking a large number of lamellared structures, and Fig. 1(b) displayed the lamellared edge was curled and intermediate region was cracked. The TEM test was carried out after the sample proceeding ultrasonic treatment in anhydrous alcohol for 30 min, and the
Conclusions
In summary, novel amorphous ternary Co-Ni-Cu hydroxide was prepared by one-step coprecipitation method, and low overpotential, rapid OER rate, low charge transfer resistance and good catalytic stability of CNC835 was confirmed by LSV, Tafel, EIS and i-t curve in 0.1 M KOH versus Ag/AgCl.
CRediT authorship contribution statement
Hongying Li: Conceptualization, Methodology, Investigation, Data curation, Writing - original draft. Xueliang Wang: Conceptualization, Writing - review & editing. Tao Wang: Visualization, Software, Supervision. Mingcheng Zhao: Investigation, Validation, Resources.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgement
This work was supported by Natural Science Foundation Committee of Shandong Province, China (Nos. ZR2017MB062 and ZR2015BL014) and the National Natural Science Foundation of China (No. 21105023).
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