Atomic layer deposition (ALD) has found versatile applications in energy, environmental, and anthropogenic systems. The self‐terminating surface chemistry characteristic of ALD allows for atomic‐level control over film thickness and has unlocked attractive avenues for the development of novel nanostructured systems. Substantial modifications of standard ALD processes are achieved with the advent of powder coating technology using ALD. The basic principle of ALD is demonstrated along with a focus on the significant parameters governing the process in order to achieve good surface characteristics. The aim of this review is to explore the challenges faced in the development of reactors for powder coatings and solve the problems associated with particle distribution in the reactors. A theoretical briefing on the agglomeration phenomena in particles is provided for a better understanding of the typical particle sizes and their distributions in reactor systems. The gradual improvement in reactor designs, with particular emphasis on the homogeneous distribution of particles, is also discussed. Conclusively, the authors also review the emerging applications where this technology is being explored to overcome surface defects through the control of atomic growth on particles.
traditional battery systems. [10,11] Practically, lower energy density bounds the applicability of supercapacitors over battery systems, leaving more room in developing high energy density supercapacitors without having to compromise the power competence. [12-14] A well-known approach offering such outstanding energy density is via fabrication of asymmetric supercapacitor device that focusses on the positive materials excellency exhibiting high specific capacitance and providing a broad potential window when combined with a double-layer type negative electrode material. [15-17] Co 3 O 4 , a pseudocapacitive metal oxide, belonging to the family of spinel is a promising positive active material in electrochemical energy storage devices owing to its high specific capacitance (3560 F g −1) theoretically with being earthabundant, cost-effective, and also environment friendly. [18-20] Pseudocapacitors follow faradaic redox electrochemical reactions on the material's surface through continuous intercalation/deintercalation of electrons or ions which makes the surface vulnerable to destruction resulting in lower efficiency of the electroactive material affecting the electrochemical cycles. [21-23] Therefore, much effort has been put forward to increase the efficiency and stability of the Co 3 O 4 structures through nanostructured, [18] heterostructured, [24,25] and core-shell type structures [26] to reduce the structural deterioration from Co 3 O 4 and increase the overall specific capacitances. For instance, a 3D hierarchical structure of CoWO 4 /Co 3 O 4 was developed that exhibited significantly high specific capacitance of 1728 F g −1 at a current density of 1 A g −1 retaining about 85.9% specific capacitance after 5000 cycles. [27] Paliwal and Meher design a heterostructure of Co 3 O 4 /NiCo 2 O 4 perforated nanosheets that delivers specific capacitance of 1767 F g −1 at a current density of 0.5 A g −1 maintaining 552 F g −1 capacitance at high current density 16 A g −1. Additionally, the asymmetric device composed of Co 3 O 4 /NiCo 2 O 4 ||N-rGO retains 93.8% areal capacitance after 10 000 operating cycles. [28] An excellent core-shell type CoO@Co 3 O 4 nanocrystals were grown solvothermally which delivered 3377 F g −1 specific capacitance at current density 2 A g −1 and the capacity retention was about 58.6% after 4000 charge-discharge cycles. [29] Lu et al. reported Co 3 O 4 /CoS core-shell nanosheets grown over Ni-foam by room temperature sulfurization process. The structure showed an improved specific capacitance as high as 1658 F g −1 at 1 A g −1 Designing of multicomponent transition metal oxide system through the employment of advanced atomic layer deposition (ALD) technique over nanostructures obtained from wet chemical process is a novel approach to construct rational supercapacitor electrodes. Following the strategy, core-shell type NiO/Co 3 O 4 nanocone array structures are architectured over Ni-foam (NF) substrate. The high-aspect-ratio Co 3 O 4 nanocones are hydrothermally grown over NF following the p...
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