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Zhang et al. Soft Sci. 2026, 6, 16 Page 3 of 17

bias voltage and deposition time. The electrochemical properties, especially the specific capacitance and
capacitance retention of the electrodes before and after coating, were emphasized. To clarify the energy
storage mechanism, the relationship among the sp2/sp3 ratio, the electrical properties, and the
electrochemical properties of carbon film-coated anodized SS electrodes was analyzed and discussed in detail
based on the characterization results. Meanwhile, an all-solid-state flexible supercapacitor device based on
the carbon film-coated anodized SS electrode was assembled to power small appliances, demonstrating
excellent practical performance as a flexible electrode.

EXPERIMENTAL

Materials
All chemicals were used directly without purification or additional treatment. Ethanol (C H O, 99.7%),
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ethylene glycol (EG, C H O , 99.5%) and ammonium fluoride (NH F, 96.0%) were obtained from Sinopharm
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2
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Chemical Reagent Co., Ltd. (Shanghai, China). Potassium persulfate (KPS, K O S , 99.9%) and acrylamide
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(AM, C H NO, 99.9%) were purchased from Shanghai Acmec Biochemical Co., Ltd. (Shanghai, China).
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N,N′-methylenebisacrylamide (MBA, C H N O , 99.0%), 304 SS foil (0.05 mm thick), silica wafer (4-inch
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type, 0.525 mm thick) and CC (0.17 mm thick) were acquired from Shanghai Aladdin Biochemical
Technology Co., Ltd. (Shanghai, China). Activated carbon (AC, YP80F specific surface area
1,900-2,250 m ·g ) was purchased from Canrd Technology Co.Ltd. (Dongguan, China). Small items,
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including a multifunctional timer and a baby’s toy, were provided by Runcheng Hardware Store (Dongguan,
China) and Didai Toy Factory (Shantou, China), respectively.
Electrode preparation
The SS foils and silica wafers were cut into 20 mm squares and then subjected to ultrasonic baths in ethanol
and deionized (DI) water for 10 min each. The cleaned SS foil was processed using a simple anodic oxidation
method described in our previous work . Briefly, the sample was fabricated by an anodization procedure in
[5]
a two-electrode electrochemical cell, where a SS foil served as the anode, a graphite plate as the cathode, a
solution containing 0.3700 g NH F, 98 mL EG, and 2 mL DI water as the electrolyte. The whole anodization
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procedure was conducted at 60 V for 2 h with an optimized parameter. After being carefully rinsed in
ethanol, the electrodes were annealed at 500 °C for 1 h for stabilization. The as-fabricated electrode was
named C-0 in the following characterizations and performance tests.
The carbon film was sputtered through an ECR plasma nano-surface manufacturing device. The anodized SS
foil was placed into the chamber of the ECR system, followed by reducing the background vacuum below
5.00 × 10 Pa. As the working gas, dry argon gas was introduced to the chamber until the pressure stabilized
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at 4.00 × 10 Pa. The plasma was generated by the combined effect of a closed electromagnetic field formed
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by a microwave (2.45 GHz, 200 W) and double magnetic coils (420 A), with the target bias voltage set at
-300 V. Three types of substrate direct current (DC) bias, -5, +20, and +100 V, were applied for a 10-min
deposition process and labeled as C-1, C-2, and C-3 [Figure 1]. The loading mass of the energy storage
material was approximately 0.0021 g per electrode. Another carbon film sample was deposited on the surface
of a silica wafer under the same parameters for thickness, Raman, and resistivity characterization. Moreover,
to investigate the influence of deposition time on capacitance performance, three additional electrodes were
sputtered for 5, 10 (C-3), and 20 min with a bias of +100 V.

All-solid-state flexible supercapacitor assembly
To explore its potential for flexible energy storage, an all-solid-state supercapacitor was constructed using a
combination of a CC anode coated with AC (AC@CC, 15 × 10 × 0.17 mm, 0.0693 g), a carbon film-coated
anodized SS cathode (15 × 10 × 0.05 mm, 0.0856 g), and a polyacrylamide (PAM)/Na SO gel electrolyte (15 ×
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10 × 1 mm in size, 0.3691 g). The total weight of the flexible supercapacitor was 3.9274 g, including the

polyethylene terephthalate seal and copper tape.