Synthesis of Hierarchical Cobalt Phosphate Nanoflakes and Their Enhanced Electrochemical Performances for Supercapacitor Applications

Abstract

Hierarchical structured cobalt phosphate (Co 3 (PO 4 ) 2 ) nanoflakes were synthesized by simple co-precipitation method and employed as electrodes for supercapacitor. The purity and phase formation of the synthesized (Co 3 (PO 4 ) 2 ) nanoflakes were ascertained by XRD and XPS measurements. The surface morphology and elemental composition of the Co 3 (PO 4 ) 2 nanoflakes were observed by using FE-SEM, TEM and EDS. The electrochemical behaviour of the present material as an anode material for supercapacitor was explored by cyclic voltammetric measurements and galvanostatic charge-discharge analysis. The specific capacitance for the as-synthesized and calcined (Co 3 (PO 4 ) 2 ) nanoflakes electrodes was 132 and 210 Fg À1 at a scan rate of 10 mV s À1 . The enhanced electrochemical behaviour of the calcined Co 3 (PO 4 ) 2 nanoflakes might be due to its well crystalline nature which offers more active sites for faradaic reactions, good conductivity and rapid diffusion of the electrolyte ions. The fabricated Co 3 (PO 4 ) 2 electrode displayed an excellent cyclic stability with 95 % retention of initial specific capacitance after 800 cycles. An enhanced effect on the electrochemical properties of the Co 3 (PO 4 ) 2 nanoflakes has been proposed.

Synthesis and Electrochemical Performances of γ‐KCoPO4 Nanocrystals as Promising Electrode for Aqueous Supercapatteries

“…However, the hydrated radius of K + (3.31 Å) ions is larger than the other two electrolytes of 1 M LiOH (3.82 Å) and 1 M NaOH (3.58 Å), since the hydrated K + ions induce more ionic conductivity between the layered structures of the electrode material which enhances the Faradaic reaction. The observed specific charge capacity of KCoPO 4 (289 C g −1 at 2 mV s −1 ) in 1 M KOH is higher and comparable than the previously reported cobalt phosphates including NaCoPO 4 (100 C g −1 at 2 mV s −1 ) and Co 3 (PO 4 ) 2 (76 C g −1 at 10 mV s −1 ) …”

Metal Phosphides and Phosphates‐based Electrodes for Electrochemical Supercapacitors

“…Chemical Precipitation Method : In the chemical precipitation process of metal phosphates, the desired component is precipitated in a solution, where it involves liquid mixing/supersaturation, nucleation, crystal growth, and aggregation of the primary particles . As a mild, relatively simple and generally green approach, the chemical precipitation approach has the advantages of: i) low energy consumption, where the reaction can be conducted even at room temperature; ii) non‐toxic reagents; and iii) time‐saving . For example, cobalt phosphate Co 3 (PO 4 ) 2 nanoflakes, Co 3 (PO 4 ) 2 ·8H 2 O micro‐flowers, and Co 3 P 2 O 8 ·8H 2 O particles were synthesized by the precipitation processes.…”

“…As a mild, relatively simple and generally green approach, the chemical precipitation approach has the advantages of: i) low energy consumption, where the reaction can be conducted even at room temperature; ii) non‐toxic reagents; and iii) time‐saving . For example, cobalt phosphate Co 3 (PO 4 ) 2 nanoflakes, Co 3 (PO 4 ) 2 ·8H 2 O micro‐flowers, and Co 3 P 2 O 8 ·8H 2 O particles were synthesized by the precipitation processes. Other metal phosphates included nickel phosphates and manganese phosphates .…”

“…P2 was shown to lead to a higher specific capacitance, better rate capability and longer cycling life. Another example, is the effect of crystallinity nature, which was investigated by studying the electrochemical behavior of the samples calcined differently. The Co 3 (PO 4 ) 2 nanoflakes of high crystallinity exhibited an enhanced specific capacitance (210 F g −1 at 10 mV −1 ), when compared with the as‐synthesized sample (132 F g −1 ) without proper calcination, together with better rate capability, arising from the improved conductivity.…”

“…The Co 3 (PO 4 ) 2 nanoflakes of high crystallinity exhibited an enhanced specific capacitance (210 F g −1 at 10 mV −1 ), when compared with the as‐synthesized sample (132 F g −1 ) without proper calcination, together with better rate capability, arising from the improved conductivity. Besides the nanosheets structure, Xi et al reported the successful synthesis of 1D nanowire amorphous cobalt phosphate, which was converted from amorphous ultrathin nanosheets by the temporal evolution through a split process. The Co 3 (PO 4 ) 2 ultrathin nanowires showed an extraordinary pseudocapacitive performance with the specific capacitance of up to 1174 F g −1 being achieved.…”