*Article* **Mesopore-Rich Activated Carbons for Electrical Double-Layer Capacitors by Optimal Activation Condition**

#### **Hye-Min Lee 1,2, Kay-Hyeok An 3,\*, Soo-Jin Park 2,\* and Byung-Joo Kim 1,\***


Received: 18 March 2019; Accepted: 10 April 2019; Published: 12 April 2019

**Abstract:** In this study, activated polymer-based hard carbon using steam activation (APHS) with mesopore-rich pore structures were prepared for application as electrodes in electrical double-layer capacitors (EDLC). The surface morphologies and structural characteristics of APHS were observed using scanning electron microscopy and X-ray di ffraction analysis, respectively. The textural properties were described using Brunauer-Emmett-Teller and Barrett-Joyner-Halenda equations with N2/77 K adsorption isotherms. APHS were prepared under various steam activation conditions to find optimal ones, which were then applied as electrode materials for the EDLC. The observed specific surface areas and total pore volumes of the APHS were in the range 1170–2410 m<sup>2</sup>/g and 0.48–1.22 cm<sup>3</sup>/g, respectively. It was observed that pore size distribution mainly depended on the activation time and temperature, and that the volume of pores with size of 1.5–2.5 nm was found to be a key factor determining the electrochemical capacity.

**Keywords:** hard carbon; steam activation; polymeric precursor; electrical double-layer capacitor
