High-density carbon tube nanoarray design enables miniaturization of filter capacitors

The research team has constructed high-density 3D carbon tube electrode nanoarrays for use in network filter capacitors. These electrodes have great potential as efficient, miniaturized filtering devices.

The research results were published in Nano-Micro letters.

Filter capacitors are essential for converting alternating voltage signals into constant direct current. Aluminum electrolytic capacitors (AEC) are widely used, but they are quite large and have limited capacitance, making it difficult to downsize in modern electronics.

Electric double layer capacitors (EDLC) have much higher energy density, making them a promising alternative for smaller filter capacitor applications. However, traditional carbon EDLC capacitors have slow ion transport, making it difficult for them to achieve both the high energy density and fast frequency response needed for linear filtering.

A team led by Prof. Meng Guowen and Prof. Han Fangming from Hefei Institutes of Physical Science of the Chinese Academy of Sciences, together with Prof. Wei Bingqing from the University of Delaware and Prof. Li Xiaoyan from Tsinghua University, conducted a systematic study to precisely manipulate the pore structure of three-dimensional interconnected porous anodized alumina (3D-AAO) templates.

They accomplished a remarkable feat by continuously tuning the vertical pore diameter of 3D-AAO from 70 to 250 nm and the interpore spacing from 100 to 450 nm. Using these tunable templates, they fabricated 3D compactly arranged carbon nanoarray tube electrodes (3D-CACT) via chemical vapor deposition.

Surface area studies have shown that reducing the pore diameter and the spacing between them significantly increased the electrode surface area.

The resulting 3D-CACT electrode-based device demonstrated exceptional frequency response, characterized by a phase angle of -80.2° at 120 Hz, an extremely low equivalent series resistance of less than 0.07 Ω cm²and a fast resistance-capacitance time constant of 0.25 ms.

It is worth noting that its specific surface capacitance at a frequency of 120 Hz reached 3.23 mF cm^-2significantly outperforming commercial AECs (~0.08 mF cm^-2) and previously reported aqueous sandwich-type EDLC line filters. This highlights the ability of 3D-CACT nanoarrays to facilitate efficient ion transport and offer numerous charge adsorption sites.

Moreover, the researchers demonstrated the scalability of their approach by connecting six and 10 sets of identical 3D-CACT-based EDLC capacitors in series, which allowed for effectively extending the operating voltage of the capacitors while maintaining fast frequency response and low losses.

To demonstrate the practicality of their invention, they used 10 series-connected filter devices to efficiently convert various AC input signals (including sine waves, square waves, triangle waves, noisy waves, and pulse signals from a rotating triboelectric nanogenerator) into smooth DC signals, with filtering performance comparable to commercial AECs.

“High-density 3D-CT nanoarray electrodes offer promising solutions for high-performance filter capacitors, advancing miniaturized power systems and electronics,” said Prof. Meng, “and the template-assisted structural method enables the size-tuning of nanomaterials and promotes the innovative development of integrable microdevices.”