Nanostructured Boron-Doped Ultra-Nanocrystalline Diamond Micro-Pyramids: Efficient Electrochemical Supercapacitors

Abstract

The miniaturization of electrochemical supercapacitors (EC-SCs) requires electrode materials that are both durable and efficient. Boron-doped diamond (BDD) films are an ideal choice for EC-SC due to their durability and exceptional electrochemical performance. In this study, nanostructured boron-doped ultra-nanocrystalline diamonds (NBUNCD) are fabricated on Si micro-pyramids (Si_P) using a simple reactive ion etching (RIE) process. During the etching process, the high aspect ratio and the induction of sp² graphite in these nanorod electrodes achieved a maximum specific capacitance of 53.7 mF cm^-2 at a current density of 2.54 mA cm^-2, with a 95.5% retention after 5000 cycles. Additionally, the energy density reached 54.06 µW h cm^-2 at a power density of 0.25 µW cm^-2. A symmetric pouch cell using NBUNCD/Si_P exhibited a specific capacitance of 0.23 mF cm^-2 at 20 µA cm^-2, an energy density of 31.98 µW h cm^-2, and a power density of 0.91 µW cm^-2. These superior EC properties highlight NBUNCD/Si_P's potential for advancing miniaturized supercapacitors with high capacitance retention, cycle stability, and energy density.

Keywords: boron; graphite; micro‐pyramids; nanorods; supercapacitors; ultra‐nanocrystalline diamond.

Figure 1

Schematic representation of the fabrication of nanostructured BUNCD on Si micro‐pyramids.

Figure 2

FESEM micrographs a) micro‐pyramidal Si substrate, b) BUNCD/Si_P, and c) NBUNCD/Si_P with (a_I, b_I, c_I) 45° angle view, (a_II, b_II, c_II) plan‐view, and (a_III, b_III, c_III) cross‐sectional view.

Figure 3

Schematic representation of the mechanism of nanostructure fabrication on BUNCD films using RIE.

Figure 4

a) Raman spectra and b) XPS spectra of C1s and c) XPS spectra O1s deconvoluted peaks of BUNCD samples for I. BUNCD/Si, II. BUNCD/Si_P, and III. NBUNCD/Si_P.

Figure 5

Cyclic voltammogram study in 1 m Na₂SO₄ at varied scan rates from 10–100 mV s⁻¹ of BUNCD samples, a) BUNCD/Si, b) BUNCD/Si_P, c) NBUNCD/Si_P, and d) a comparison of the current response of these BUNCD samples at 60 mV s⁻¹.

Figure 6

Galvanostatic charging‐discharging study with varying current densities in 1 m Na₂SO₄ of BUNCD samples, a) BUNCD/Si, b) BUNCD/Si_P, c) NBUNCD/Si_P, and d) a comparison of electrochemical impedance spectra of these BUNCD samples with the inset showing the equivalent circuit fitted to the EIS spectra for I. BUNCD/Si, II. BUNCD/Si_P, and III. NBUNCD/Si_P.

Figure 7

Cyclic voltammogram study in 0.05 m [Fe(CN)₆]^3−/4− contained in 1 m Na₂SO₄ at varied scan rates from 10–100 mV s⁻¹ of BUNCD samples, a) BUNCD/Si, b) BUNCD/Si_P, c) NBUNCD/Si_P, and d) a comparison of the current response of these BUNCD samples at 60 mV s⁻¹.

Figure 8

Galvanostatic charging‐discharging study with varying current densities in 0.05 m [Fe(CN)₆]^3−/4− contained in 1 m Na₂SO₄ of BUNCD samples, a) BUNCD/Si, b) BUNCD/Si_P, c) NBUNCD/Si_P.

Figure 9

Electrochemical Impedance Spectroscopy in 0.05 m Fe(CN)₆ ^3−/4− contained in 1 m Na₂SO₄ of BUNCD samples, a) BUNCD/Si, b) BUNCD/Si_P, and c) NBUNCD/Si_P, with (a_I, b_I, c_I) EIS spectra and (a_II, b_II, c_II) corresponding equivalent circuit for the EIS spectra.

Figure 10

Retention of specific capacitance a,b) and Coulombic efficiency c,d) of the BUNCD samples calculated from 5000 cycles of charging−discharging in (a,c) 1 m Na₂SO₄ and (b,d) 0.05 m [Fe(CN)₆]^3−/4− contained in 1 m Na₂SO₄, I. BUNCD/Si, II. BUNCD/Si_P, and III. NBUNCD/Si_P.

Figure 11

Schematic representation of the symmetric pouch cell with NBUNCD/SiP, shown in the inset of (a), along with (a) cyclic voltammetry, b) galvanostatic charge‐discharge curve, and c) life cycle stability measurement (inset showing specific capacitance calculations from (b)) of the symmetric cell using NBUNCD/SiP in 3 m KOH.