Hierarchical Structure MnO₂ Coated PDMS−Carbon Nanotube Sponge as Flexible Electrode for Electrocatalytic Water Splitting and High Performance Supercapacitor

Abstract

As a typical transition metal oxide, MnO2 has great potential in catalysis and energy storage, but its poor conductivity greatly limits its performance. PDMS−carbon nanotube sponges have excellent electrical conductivity and flexibility. Herein, according to the principle of complementary, we propose a novel hierarchical PDMS−carbon nanotube sponge@MnO2 electrode with uniform size and morphology. In view of the structural preponderances and multifunctional of the materials, the PDMS−carbon nanotube sponge@MnO2 has been investigated as the binder−free electrode materials for both supercapacitors and electrocatalysis applications. PDMS−carbon nanotube sponge@MnO2 electrode exhibits an admirable HER property with a low onset potential of 112 mV at −30 mA cm−2, a minimal overpotential (η=258 mV), a small Tafel slope (71 mV dec−1), large anodic currents and stability for 20 h in 0.1 M H2SO4 solution. Moreover, as supercapacitor electrode, the PDMS−carbon nanotube sponge@MnO2 electrode achieves a specific mass capacitance reaching 124.7 mF cm−2 at 1 A cm−2 and good flexibility, which are better than those ternary transition metal oxides. The assembled asymmetric device with the PDMS−carbon nanotube sponge@MnO2 and CNTs respectively as positive and negative electrode has a large window voltage of 1.4 V, and thus acquires an expected specific mass capacitance (422 mF cm−3 at the current density of 1 A cm−3) and an outstanding higher energy density of 15.3 W h kg−1 (at 371 W kg−1).

Carbon Transition‐metal Oxide Electrodes: Understanding the Role of Surface Engineering for High Energy Density Supercapacitors

“…Song et al prepared hierarchical MnO 2 coated on PDMS-CNT (polydimethylsiloxane-carbon nanotube) sponge by a two-step technique shown in Figure 2(c) involving physical mixing and thermal treatment. [62] The PDMS-CNT sponge was mixed with KMnO 4 and calcined at 200°C to obtain the PDMS-CNT sponge@MnO 2 composite. Core-shell heterostructured MnO x nanowires@C@MnO x nanosheets were reported by Ma et al [63] MnO 2 @PDA (dopamine hydrochloride) was precipitated from buffer solution containing hydrothermally pre-synthesized MnO 2 nanowires, followed by aging in a solution containing Mn salt to obtain MnO 2 nanowire@PDA@MnO 2 nanosheet, which subsequently converted into MnO 2 nanowire@C@MnO2 nanosheet upon calcination under N 2 at 300°C.…”

“…Various synthetic routes have been reported for the fabrication of binder-free electrode composed of carbon substrate (e. g. carbon foam, CNT film, 3D graphene foam, carbon paper/cloth, or biomass-derived carbon) and transition metal oxides as pseudocapacitive materials to achieve high energy density supercapacitor. [62,67,98,99] Carbon coated sponges/foams with 3D porous structure have been considered as potential carbon substrate since their inner and outer surfaces are suitable for the deposition of active materials, and their general properties including lightweight, great flexibility and low cost make them more attractive. [62,100] In addition, the macroporosity and high-surface area of these materials promote the facile electrolyte-electron movement even at very high rates.…”

“…[62,67,98,99] Carbon coated sponges/foams with 3D porous structure have been considered as potential carbon substrate since their inner and outer surfaces are suitable for the deposition of active materials, and their general properties including lightweight, great flexibility and low cost make them more attractive. [62,100] In addition, the macroporosity and high-surface area of these materials promote the facile electrolyte-electron movement even at very high rates. 3D-CNT sponge and graphene foam, both of them possessing low density, high electrical conductivity, and excellent mechanical properties, are considered to be ideal electrode material.…”