Supporting Information

Rapid single-step synthesis of porous carbon from an agricultural waste

for energy storage application

Weimin Chena,b, Xin Wanga,b, Chaozheng Liua,b, Min Luoa,b, Pei Yanga,b, and Xiaoyan Zhoua,b*

aCollege of Materials Science and Engineering, Nanjing Forestry University, Nanjing

210037, China;

bJiangsu Engineering Research Center of Fast-growing Trees and Agri-fiber Materials,

Nanjing 210037, China;

*Corresponding author: Tel.: +86 25 8542 8506; Fax: +86 25 85428518; E-mail:

zhouxiaoyan@njfu.edu.cn; Postal address: No. 159, Longpan Road, Nanjing, Jiangsu

Province, China, 210037

Keywords: Wheat straw; Char; Microwave; Porous carbon; Supercapacitor.

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Figures

Fig. S1. Diagram of the prepared supercapacitor.

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Fig. S2. Temperature profiles of the reactor as a function of microwave heating duration.

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Fig. S3. Pore structure of CPC: (a) N2 adsorption-desorption isotherms, (b) pore size distribution by DFT

method.

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Fig. S4. TEM images: (a) PC-10 and (b) PC-20.

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Fig. S5. Surface chemical properties of PCs: (a) O-containing chemical groups in carbon framework, and

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(b) O1s spectra.

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Fig. S6. The low-resulotion spectra of the compared PC prepared in a tubular furnace with the folloing

conditions: a mass ratio (wheat straw: wheat straw-derived char: KOH) of 1:1:6, a heating rate of 10 °C

min−1 to 630 °C and held for 1h, as well as by single-step contact heating.

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Fig. S7. CV profiles of (a) PC-10 and (b) PC-20.

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Fig. S8. Capacitive performances of the electrode based on wheat straw char-derived porous carbon in 6

mol L-1 KOH electrolyte using three-electrode configuration: (a) CV profiles, (b) rate capability, insert:

GCD curve at 0.5 A g-1, (c) Nyquist plots.

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Fig. S9. CV profiles at operational potential ranges, and tested at a scan rate of 50 mV s−1.

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Tables

Table S1. Proximate and elemental compositions of wheat straw and its derived char.

Content (%)

Wheat straw Wheat straw-derived char

Proximate compositiona

Moistureb 8.2 5.3

Volatilesc 62.1 19.8

Fixed carbond 23.4 58.3

Ashe 6.3 16.6

Elemental compositionf

C 43.7 67.2

H 5.8 0.9

O 37.1 8.4

N 0.9 0.7

Sh 0 0

a Dry basis,

b, c Determined using a thermogravimetric analyzer (STA449C, Netzsch),

d Determined by difference,

e Determined after calcination in a tubular furnace at 800 °C for 1h,

f Dry ash-free basis and Determined using an elemental analyzer (2400 , PerkinElmer),Ⅱ

h Not detectable,

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Table S2. Estimation for production costa.

Item Estimated cost for single-step synthesis

Microwave heating for PC-50 Conventional contact heatingb

Raw material

Waste wheat straw 0.5 CNY kg−1

Wheat-straw-derived charc 1.1 CNY kg−1

Transportation 0.1 CNY kg−1

Cost (0.5 kg * 0.5 CNY kg−1 + 0.5 kg * 1.1 CNY

kg−1) + 1 kg * 0.1 CNY kg−1 = 0.9 CNY

0.5 kg * 1 CNY kg−1 + 1 kg *

0.1 CNY kg−1 =0.6 CNY

Electrical consumption

Yield amount 26 wt% Yield * (0.5 kg wheat straw + 0.5

kg char) = 0.26 kg

15 wt% Yield * 1 kg wheat

straw = 0.15 kg

Batch 15 (1 kg/0.07 kg batch−1=14.3) 1d

Electricity 0.8 CNY (kW h)−1

Output power 0.8 kW 4.0 kW

Heating consumption 15 batch * 0.8 kW * (5/60) h = 1.00 kW h 1 batch * 4.0 kW * (137.5/60) h

≈ 9.17 kW h

Cost 1.00 kW h * 0.8 CNY (kW h)−1 = 0.8 CNY 9.17 kW h * 0.8 CNY (kW h)−1

= 7.3 CNY

Total cost (0.9 CNY + 0.8 CNY)/0.26 kg ≈ 6.54 CNY

kg−1

(0.6 CNY + 7.3 CNY)/0.15 kg ≈

52.67 CNY kg−1

a The same items between these two approach such as chemical activating agent were not included,

b A typical production procedure was used in conventional contact heating: wheat straw was heated from

room temperature to 800 °C and held for 1h at a heating rate of 10 °C min−1,

c For large-scale production, commercial wheat-straw-derived char can be used directly, since it only

acted as microwave absorber during microwave irradiation,

d The conventional contact heating can use a much larger reactor than that of microwave heating, since

there is a long holding duration to ensure sufficient activation.

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