Nowadays, the increasing requirements of portable, implantable, and wearable electronics have greatly stimulated the development of miniaturized energy storage devices (MESDs). Electrochemically active materials and microfabrication techniques are two indispensable parts in MESDs. Particularly, the architecture design of microelectrode arrays is beneficial to the accessibility of two-dimensional (2D) active materials. Therefore, this study reviews the recent advancements in microbatteries and microsupercapacitors based on electrochemically active 2D materials. Emerging microfabrication strategies enable the precise control over the thickness, homogeneity, structure, and dimension in miniaturized devices, which offer tremendous opportunities for achieving both high energy and power densities. Furthermore, smart functions and integrated systems are discussed in detail in light of the emergence of intelligent and interactive modes. Finally, future developments, opportunities, and urgent challenges related to 2D materials, device fabrications, smart responsive designs, and microdevice integrations are provided.

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Two-dimensional materials for miniaturized energy storage devices: from individual devices to smart integrated systems

Summary Transition metal dichalcogenides (TMDs) are promising materials for use in electrocatalytic and electrochemical energy-storage systems owing to their exceptional physicochemical properties, including large surface area, remarkable mechanical properties, high catalytic activity, chemical stability, and low cost. In further improving material properties tailored to meet application-specific requirements, heterostructure construction holds significant advantages, benefiting from the synergistic effect between constituents involved. TMD-based heterostructures have been widely explored recently, giving rise to diverse materials with desirable characteristics such as significantly increased interfacial contact of low resistance for efficient electron transfers, constituent-dependent electronic structure, tunable layer distances facilitating easily intercalation of redox species, and increased surface area for effective interaction with electrolyte. In this review, TMD-based heterostructures are assessed for performance in electrocatalytic conversion (hydrogen evolution reaction) and electrochemical energy-storage systems (NiB/LiB/supercapacitors). The impactful strategies employed in overcoming key challenges are evaluated, and finally, future directions for TMD-based heterostructure construction are presented.

Design Strategies for Development of TMD-Based Heterostructures in Electrochemical Energy Systems

On-chip micro-supercapacitors (MSCs), as promising power candidates for microdevices, typically exhibit high power density, large charge/discharge rates, and long cycling lifetimes. However, as for most reported MSCs, the unsatisfactory areal energy density (<10 µWh cm-2 ) still hinders their practical applications. Herein, a new-type Zn-ion hybrid MSC with ultrahigh areal energy density and long-term durability is demonstrated. Benefiting from fast ion adsorption/desorption on the capacitor-type activated-carbon cathode and reversible Zn stripping/plating on the battery-type electrodeposited Zn-nanosheet anode, the fabricated Zn-ion hybrid MSCs exhibit remarkable areal capacitance of 1297 mF cm-2 at 0.16 mA cm-2 (259.4 F g-1 at a current density of 0.05 A g-1 ), landmark areal energy density (115.4 µWh cm-2 at 0.16 mW cm-2 ), and a superb cycling stability without noticeable decay after 10 000 cycles. This work will inspire the fabrication and development of new high-performance microenergy devices based on novel device design.

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Zn-Ion Hybrid Micro-Supercapacitors with Ultrahigh Areal Energy Density and Long-Term Durability.

To achieve high energy and power density simultaneously in miniaturized electronic devices, a zinc-ion micro-supercapacitor (ZmSC) is constructed for the first time by integrating a battery-type zinc micro-anode and a capacitor-type carbon nanotube micro-cathode. In the meantime, an electroplating method is developed to in situ replenish the zinc anode when needed without destroying the configuration of the ZmSC, in which the micro-cathode, micro-anode and electrolyte of the ZmSC function as the working electrode, counter electrode and plating solution in the plating process, respectively. This strategy effectively avoids the irreversible consumption of the zinc anode and the fading of the capacitance and cycle life. As a result, the prepared ZmSC exhibits an excellent electrochemical performance, including a high area capacitance of 83.2 mF cm−2 at 1 mA cm−2, a high energy density of 29.6 μW h cm−2 and a high power density of 8 mW cm−2. After 6000 cycles, the ZmSC shows about 87.4% retention (60.9 mF cm−2) of its initial area capacitance at 5 mA cm−2. Furthermore, a higher capacitance (76 mF cm−2) and a longer cycling life are obtained after re-plating the zinc anode. This method features a simple configuration and easy operation, and holds great promise for use in other long cycle life zinc-based microdevices.

A capacity recoverable zinc-ion micro-supercapacitor

Superior mixed Co-Cd selenide nanorods for high performance alkaline battery-supercapacitor hybrid energy storage

A novel process to fabricate a carbon-microelectromechanical-system-based alternating stacked MoS2@rGO–carbon-nanotube (CNT) micro-supercapacitor (MSC) is reported The MSC is fabricated by successively repeated spin-coating of MoS2@rGO/photoresist and CNT/photoresist composites twice, followed by photoetching, developing, and pyrolysis MoS2@rGO and CNTs are embedded in the carbon microelectrodes, which cooperatively enhance the performance of the MSC The fabricated MSC exhibits a high areal capacitance of 137 mF cm−2 and an energy density of 19 µWh cm−2 (56 mWh cm−3), which exceed many reported carbon- and MoS2-based MSCs The MSC also retains 68% of capacitance at a current density of 2 mA cm−2 (59 A cm−3) and an outstanding cycling performance (966% after 10 000 cycles, at a scan rate of 1 V s−1) Compared with other MSCs, the MSC in this study is fabricated by a low-cost and facile process, and it achieves an excellent and stable electrochemical performance This approach could be highly promising for applications in integration of micro/nanostructures into microdevices/systems

Carbon-MEMS-Based Alternating Stacked MoS2@rGO-CNT Micro-Supercapacitor with High Capacitance and Energy Density

Rationally generating oxygen vacancies in electrocatalysts is an important approach to modulate the electrochemical activity of a catalyst. Herein, we report a remarkable enhancement in oxygen reduction reaction (ORR) activity of NiCo2O4 supported on hollow carbon spheres (HCS) achieved through generating abundant oxygen vacancies within the surface lattice. This catalyst exhibits enhanced ORR activity (larger limiting current density of ∼−5.8 mA cm–2) and higher stability (∼90% retention after 40 000 s) compared with those of NiCo2O4/HCS and NiCo2O4. The results of X-ray photoelectron spectroscopy (XPS) characterizations suggest that the introduction of oxygen vacancies optimizes the valence state of active sites. Furthermore, we carried out density functional theory (DFT) calculations to further confirm the mechanism of oxygen vacancies, and results show that oxygen vacancies enhance the density of states (DOS) near the Fermi level, decrease work function, and lower the calculated overpotential of NiCo2O4.

Oxygen Vacancy-Determined Highly Efficient Oxygen Reduction in NiCo2O4/Hollow Carbon Spheres

Constructing on-chip microsupercapacitors (MSCs) with an asymmetric structure is the predominant choice for applications in miniaturized electronic devices. However, the complex fabrication methods of electrodes and the assembling process of devices restrict the development of on-chip MSCs. Herein, a planar asymmetric MSC with MnxCo1−x(OH)2 nanosheet arrays as the cathode and Fe3O4 nanoparticles as the anode is fabricated via a facile one-step electrodeposition method combined with microfabrication technology. The planar asymmetric MSC exhibits a wider operation voltage window (up to 1.65 V), a higher capacitance (32 mC cm−2), and a higher energy density (7.78 μW h cm−2) than those of previously reported MSCs with an alkaline aqueous electrolyte. This work demonstrates a model of the excellent combination of material synthesis and device fabrication towards large-scale manufacture of on-chip microdevices.

One-step electrodeposited MnxCo1−x(OH)2 nanosheet arrays as cathode for asymmetric on-chip micro-supercapacitors

Microdevices: Carbon-MEMS-Based Alternating Stacked MoS2@rGO-CNT Micro-Supercapacitor with High Capacitance and Energy Density (Small 26/2017)

The invention relates to a teflon fixture for a wet process of a semiconductor micron/nano device and an application thereof. The teflon fixture comprises a first clamp plate, a second clamp plate, a first slide rod, a second slide rod and a handle, wherein the first clamp plate and the second clamp plate are disposed in parallel; one end of the first slide rod is perpendicularly fixed on the first clamp plate, and the other end of the first slide rod passes through the second clamp plate in a matched manner; one end of the second slide rod is perpendicularly fixed on the second clamp plate, and the other end of the second slide rod passes through the first clamp plate in a matched manner; the handle is fixed on the first slide rod or the second slide rod; and card slots which are matched with each other are respectively formed in surfaces, which are just opposite to each other, of the first clamp plate and the second clamp plate. The first clamp plate, the second clamp plate, the first slide rod, the second slide rod and the handle are all made from teflon materials. The fixture is simple in structure and convenient to clamp; the fixture can be applied to the wet process such as cleaning, etching, developing, rinsing, removing of photoresist and the like, of the semiconductor micron/nano device, and is high in efficiency and convenient to operate.

Hui Yuan

Papers

Carbon-MEMS-Based Alternating Stacked MoS2@rGO-CNT Micro-Supercapacitor with High Capacitance and Energy Density

Oxygen Vacancy-Determined Highly Efficient Oxygen Reduction in NiCo2O4/Hollow Carbon Spheres

One-step electrodeposited MnxCo1−x(OH)2 nanosheet arrays as cathode for asymmetric on-chip micro-supercapacitors

Microdevices: Carbon-MEMS-Based Alternating Stacked MoS2@rGO-CNT Micro-Supercapacitor with High Capacitance and Energy Density (Small 26/2017)

Teflon fixture for wet process of semiconductor micron/nano device and application thereof