Search

Highly efficient and robust electrocatalysts intended for the oxygen evolution reaction (OER) are essential for energy conversion devices; the structural and morphological fractions of the electrocatalyst can also greatly influence the OER performance. Therefore, developing a high-performing electrocatalyst with desired properties is crucial through a simple and cost-effective chemical process. So, the binder-free, hydrous cobalt phosphate (Co3(PO4)2.nH2O) thin film electrocatalysts are prepared via the successive ionic layer adsorption and reaction (SILAR) method onto stainless steel (SS) substrates at ambient temperature. Additionally, the impact of annealing on the OER efficiency of thin film electrodes made of hydrous cobalt phosphate was observed by subjecting the electrocatalysts to different temperatures (200°C and 400°C). The SILAR synthesized hydrous Co3(PO4)2.nH2O with the short-range ordered agglomerated particles transformed into discrete nanoparticles with an annealing temperature. The as-prepared hydrous cobalt phosphate (CP) demonstrated outstanding OER performance with the least overpotential (η) of 265 mV at 10 mA cm-2 current density and the lowest Tafel slope of 37 mV dec-1, and the overpotential ( η 10 ) increased upon the annealing of catalysts (CP 200 and CP 400). Moreover, the as-prepared electrocatalyst demonstrated overall water splitting at the lowest potential of 1.56 V (@10 mA cm-2) in the alkaline electrolysis system (CP//Pt). The present study reveals that the electrocatalytic performance of the as-prepared cobalt phosphate thin film catalyst is significantly associated with the hydrous content present in catalysts and demonstrates the practical applicability of SILAR-synthesized binder-free cobalt phosphate thin film electrocatalysts. [ABSTRACT FROM AUTHOR]

Rational designing of electrode materials having high surface area can accomplish the enhanced charge‐storing ability of the electrochemical energy storage devices. Therefore, the surface area of cobalt vanadium oxide (CVO) material is controlled by changing growth dynamics in successive ionic layer adsorption and reaction methods. Structural analysis confirms the formation of hydrous cobalt vanadium oxide nanoparticles (Co3V2O8⋅nH2O) thin film electrodes, and alteration in the surface area with change in growth dynamics is observed in Brunauer–Emmett–Teller analysis. The CVO1:1 thin film electrode prepared at optimal growth dynamics illustrates high specific capacitance (Cs) (capacity) of 793 F g−1 (396.7 C g−1) at 0.5 A g−1, respectively. Moreover, aqueous hybrid supercapacitor devices constructed using CVO1:1 as cathode exhibit high Cs of 133.5 F g−1 at 1.1 A g−1, specific energy (SE) of 47.7 Wh kg−1 with specific power (SP) of 0.90 kW kg−1. The solid‐state hybrid supercapacitor devices also offer high Cs of 102.9 F g−1 at 0.3 A g−1, SE of 36.6 Wh kg−1 at SP of 0.30 kW kg−1. In the SILAR approach, the dipping time plays a critical role in improving the surface area of the material and, consequently, electrochemical performance, as the current work amply indicates. [ABSTRACT FROM AUTHOR]

The binder-free synthesis of nickel–cobalt phosphate electrodes has attracted tremendous attention in hybrid energy storage devices due to their significant electrochemical activity based on the synergy between Ni and Co cations. As such, the present work describes a facile scalable synthetic approach using the potentiostatic electrodeposition (PED) of binder-free nickel–cobalt phosphate electrodes with varying Ni : Co composition. Alteration in Ni : Co composition leads to amorphous-to-crystalline structural conversion and the microsphere-to-nanosheet-like morphological evolution of nickel–cobalt phosphate electrodes. The optimal ∼1 : 1 (Ni : Co) composition nickel–cobalt phosphate electrode with clustered nanoparticle-like morphology exhibits intercalation pseudocapacitive behavior and demonstrates a maximum specific capacitance (capacity) of 2228 F g−1 (891 C g−1) at 1.5 A g−1 current density. Moreover, the fabricated aqueous hybrid asymmetric supercapacitor (AHAS) device delivers a high specific capacitance of 185 F g−1, possessing an energy density of 65.7 W h kg−1 at 2.2 kW kg−1 power density with 97% retention. Furthermore, the solid-state hybrid asymmetric supercapacitor (SHAS) device displays a maximum specific capacitance of 90 F g−1 with 32 W h kg−1 energy density at 0.32 kW kg−1 power density and exhibits 89% capacitive retention. The present study establishes a scalable synthesis of binder-free nickel–cobalt phosphate electrodes as cathodes in hybrid energy storage devices for practical applications. [ABSTRACT FROM AUTHOR]