Supercapacitors have drawn considerable attention in recent years due to their high specific power, long cycle life, and ability to bridge the power/energy gap between conventional capacitors and batteries/fuel cells. Nanostructured electrode materials have demonstrated superior electrochemical properties in producing high-performance supercapacitors. In this review article, we describe the recent progress and advances in designing nanostructured supercapacitor electrode materials based on various dimensions ranging from zero to three. We highlight the effect of nanostructures on the properties of supercapacitors including specific capacitance, rate capability and cycle stability, which may serve as a guideline for the next generation of supercapacitor electrode design.

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Supercapacitor electrode materials: nanostructures from 0 to 3 dimensions

Cerium dioxide (CeO2, ceria) is becoming an ubiquitous constituent in catalytic systems for a variety of applications. 2016 sees the 40th anniversary since ceria was first employed by Ford Motor Company as an oxygen storage component in car converters, to become in the years since its inception an irreplaceable component in three-way catalysts (TWCs). Apart from this well-established use, ceria is looming as a catalyst component for a wide range of catalytic applications. For some of these, such as fuel cells, CeO2-based materials have almost reached the market stage, while for some other catalytic reactions, such as reforming processes, photocatalysis, water-gas shift reaction, thermochemical water splitting, and organic reactions, ceria is emerging as a unique material, holding great promise for future market breakthroughs. While much knowledge about the fundamental characteristics of CeO2-based materials has already been acquired, new characterization techniques and powerful theoretical methods are dee...

Fundamentals and Catalytic Applications of CeO2-Based Materials

Using a simple hydrothermal procedure, cobalt oxide (Co3O4) nanowires were in situ synthesized on three-dimensional (3D) graphene foam grown by chemical vapor deposition. The structure and morphology of the resulting 3D graphene/Co3O4 composites were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Raman spectroscopy. The 3D graphene/Co3O4 composite was used as the monolithic free-standing electrode for supercapacitor application and for enzymeless electrochemical detection of glucose. We demonstrate that it is capable of delivering high specific capacitance of ∼1100 F g–1 at a current density of 10 A g–1 with excellent cycling stability, and it can detect glucose with a ultrahigh sensitivity of 3.39 mA mM–1 cm–2 and a remarkable lower detection limit of <25 nM (S/N = 8.5).

3D Graphene–Cobalt Oxide Electrode for High-Performance Supercapacitor and Enzymeless Glucose Detection

We report a new and general strategy for improving the capacitive properties of TiO2 materials for supercapacitors, involving the synthesis of hydrogenated TiO2 nanotube arrays (NTAs). The hydrogenated TiO2 (denoted as H–TiO2) were obtained by calcination of anodized TiO2 NTAs in hydrogen atmosphere in a range of temperatures between 300 to 600 °C. The H–TiO2 NTAs prepared at 400 °C yields the largest specific capacitance of 3.24 mF cm–2 at a scan rate of 100 mV s–1, which is 40 times higher than the capacitance obtained from air-annealed TiO2 NTAs at the same conditions. Importantly, H–TiO2 NTAs also show remarkable rate capability with 68% areal capacitance retained when the scan rate increase from 10 to 1000 mV s–1, as well as outstanding long-term cycling stability with only 3.1% reduction of initial specific capacitance after 10 000 cycles. The prominent electrochemical capacitive properties of H–TiO2 are attributed to the enhanced carrier density and increased density of hydroxyl group on TiO2 surfa...

Hydrogenated TiO2 Nanotube Arrays for Supercapacitors

Flexible solid-state supercapacitors (FSSCs) are frontrunners in energy storage device technology and have attracted extensive attention owing to recent significant breakthroughs in modern wearable electronics In this study, we review the state-of-the-art advancements in FSSCs to provide new insights on mechanisms, emerging electrode materials, flexible gel electrolytes and novel cell designs The review begins with a brief introduction on the fundamental understanding of charge storage mechanisms based on the structural properties of electrode materials The next sections briefly summarise the latest progress in flexible electrodes (ie, freestanding and substrate-supported, including textile, paper, metal foil/wire and polymer-based substrates) and flexible gel electrolytes (ie, aqueous, organic, ionic liquids and redox-active gels) Subsequently, a comprehensive summary of FSSC cell designs introduces some emerging electrode materials, including MXenes, metal nitrides, metal–organic frameworks (MOFs), polyoxometalates (POMs) and black phosphorus Some potential practical applications, such as the development of piezoelectric, photo-, shape-memory, self-healing, electrochromic and integrated sensor-supercapacitors are also discussed The final section highlights current challenges and future perspectives on research in this thriving field

Towards flexible solid-state supercapacitors for smart and wearable electronics

Large-area manganese oxide nanorod arrays (MONRAs) and herringbones (MOHBs) were successfully synthesized on F-doped SnO2 coated glass (FTO) substrates by a simple electrochemical method. Cyclic voltammetry (CV) and galvanostatic charge/discharge measurements demonstrated that the MONRAs and MOHBs exhibited excellent specific capacitance and good cycling stability in 0.5 M Na2SO4 aqueous solution. For example, the specific capacitance of the MONRAs achieves as high as 660.7 F g−1 at a scan rate of 10 mV s−1 and 485.2 F g−1 at a current density of 3 A g−1, respectively. Furthermore, the presented method may be extended to allow similar MONRs with a specific capacitance of 583.6 F g−1 to grow on flexible Ti foil, which may have great potential application in fabricating flexible supercapacitors.

Facile synthesis of large-area manganese oxide nanorod arrays as a high-performance electrochemical supercapacitor

Highly sensitive detection of urinary protein variations using tilted fiber grating sensors with plasmonic nanocoatings

In-situ DNA hybridization detection with a reflective microfiber grating biosensor.

Oriented hexagonal CeO2 NRs were directly grown on Ti substrates via a simple template-free electrochemical method. These CeO2 NRs with {110} planes as the main exposed surfaces show significant photocatalytic activity for hydrogen evolution with Na2S–Na2SO3 as sacrificial agents due to their special redox capacity.

Yunyun Huang

Papers

Facile synthesis of large-area manganese oxide nanorod arrays as a high-performance electrochemical supercapacitor

Highly sensitive detection of urinary protein variations using tilted fiber grating sensors with plasmonic nanocoatings

In-situ DNA hybridization detection with a reflective microfiber grating biosensor.

Redox cycles promoting photocatalytic hydrogen evolution of CeO2 nanorods

A label-free cardiac biomarker immunosensor based on phase-shifted microfiber Bragg grating.