New ternary-component layered double hydroxide as a low-cost and efficient electrocatalyst for water oxidation: NiCaFe-LDH from eggshell bio-waste

Herein, a new ternary-component layered double hydroxide (LDH) consisting of Ca2+ was constructed using an inexpensive bio-waste; eggshell, through a facile hydrothermal method (NiCaFe-LDH-H). The prepared material, NiCaFe-LDH-H, was characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), N-2 adsorption-desorption; Brunauer-Emmett-Teller (BET), difference thermogravimetry (DTG) and thermogravimetric analysis (TGA). Then, the NiCaFe-LDH-H was used as an electrocatalyst material to fabricate the modified carbon paste electrode (CPE) for water oxidation at neutral solutions (pH = 7.0). The electrochemical tests show that the NiCaFe-LDH-H modified CPE has efficient electrocatalytic activity towards the water oxidation reaction in a neutral solution. The effect of the LDH preparation method, presence of Ca2+ (as a low-cost material in comparison with transition metals), and its primary source was investigated on the electrocatalytic activity of the NiCaFe-LDH-H modified CPE and compared with binary-component LDHs (without Ca2+). The results of the electrochemical examinations indicate that the incorporation of Ca2+ from the eggshell source into the LDH by the hydrothermal method improve water oxidation performance of the NiCaFe-LDH-H modified CPE: lowering the onset potential to about 1.56 V vs. reversible hydrogen electrode (RHE) and overpotential to 373 mV in a neutral solution. The promoted electrocatalytic activity of the present modified CPE can be attributed to the high active surface area of the NiCaFe-LDH-H modified CPE due to the high crystallinity of LDH containing Ca2+.