Because of their availability, adjustable microstructure, varieties of forms, and large specific surface area, porous carbon materials are of increasing interest for use in hydrogen storage adsorbents and electrode materials in supercapacitors and lithium–sulfur cells from the viewpoint of social sustainability and environmental friendliness. Therefore, much effort has been made to synthesize and tailor the microstructures of porous carbon materials via various activation procedures (physical and chemical activation). In particular, the chemical activation of various carbon sources using KOH as the activating reagent is very promising because of its lower activation temperature and higher yields, and well-defined micropore size distribution and ultrahigh specific surface area up to 3000 m2 g−1 of the resulting porous carbons. In this feature article, we will cover recent research progress since 2007 on the synthesis of KOH-activated carbons for hydrogen and electrical energy storage (supercapacitors and lithium–sulfur batteries). The textural properties and surface chemistry of KOH-activated carbons depend on not only the synthesis parameters, but also different carbon sources employed including fossil/biomass-derived materials, synthetic organic polymers, and various nanostructured carbons (e.g. carbon nanotubes, carbon nanofibers, carbon aerogels, carbide-derived carbons, graphene, etc.). Following the introduction to KOH activation mechanisms and processing technologies, the characteristics and performance of KOH-activated carbons as well as their relationships are summarized and discussed through the extensive analysis of the literature based on different energy storage systems.

KOH activation of carbon-based materials for energy storage

Preparation of capacitor’s electrode from cassava peel waste

High specific capacitance and low cost are the critical requirements for a practical supercapacitor. In this paper, a new activated carbon with high specific capacitance and low cost was prepared, employing cotton stalk as the raw material, by using the phosphoric acid (H3PO4) chemical activation method. The optimized conditions were as follows: the cotton stalk and activating agent with a mass ratio of 1:4 at an activation temperature of 800 °C for 2 h. The samples were characterized by nitrogen adsorption isotherms at 77 K. The specific surface area and pore volume of activated carbon were calculated by Brunauer–Emmett–Teller (BET) and t-plot methods. With these experimental conditions, an activated carbon with a BET surface area of 1,481 cm2 g−1 and micropore volume of 0.0377 cm3 g−1 was obtained. The capacitance of the prepared activated carbon was as high as 114 F g−1.The results indicate that cotton stalk can produce activated carbon electrode materials with low cost and high performance for electric double-layer capacitor.

Preparation of activated carbon from cotton stalk and its application in supercapacitor

KOH-activated nitrogen doped porous carbon nanowires with superior performance in supercapacitors

In this study, activated carbons were synthesized from seeds of local date fruits in the United Arab Emirates (UAE) and investigated for carbon dioxide (CO2) adsorption. Activated carbon (AC) synthesis was completed by furnace activation in the temperature range (600, 700, 800, 900 °C) after infusion with chemical compounds. Two reagents (Potassium Hydroxide- KOH and Sulfuric acid- H2SO4) were mixed with the date seed samples in varying impregnation ratios (KOH- 3:1, 4:1, 5:1 and H2SO4- 0.5:1, 1:1, 2:1) and directly heated to activation wherein the removal of volatile matter content leads to formation of AC porous structure. The AC yield was found to be inversely proportional to the activating temperature and impregnating ratio. Characterization tests carried out include elemental analysis, nitrogen sorption isotherms to assess surface area and micropore volumes, and Fourier transform infrared spectra to identify structural changes in surface functional groups. Adsorption tests were conducted via a micro- reaction calorimeter using pure CO2 stream at atmospheric pressures and temperatures (20, 30, 40 °C). The sulfuric acid activated carbons showed better capture capability in the range 40–80 mgCO2/gAC while KOH- samples had low CO2 uptakes (

Synthesis and characterization of activated carbon from biomass date seeds for carbon dioxide adsorption

Preparation of high-performance activated carbons for electric double layer capacitors by KOH activation of mesophase pitches

Influences and mechanisms of phosphate ions onto persulfate activation and organic degradation in water treatment: A review.

Defect type and interactions among active sites are critical in heterogeneous peroxymonosulfate (PMS) system. Herein, a continuous flow fixed bed PMS reactor with distilled spirits lees derived biochar (DSLBs)/quartz wool was designed to explore the synergistic roles of active sites. Satisfyingly, with high graphite N, CO content and defect degree, DSLB-800 exhibited superior catalytic activity, durability and applicability for sulfamethoxazole (SMX) removal. The dominant contribution of 1O2, and minor roles of SO4•− and •OH were confirmed. Single graphite N, CO and C-O, combined interactions between graphite N and pyridine N, graphite N and pyrrole N, pyridine N and pyrrole N, CO and OC-O, OC-O and C-O, as well as interactions among graphite N, pyridine N and pyrrole N contributed to 1O2 generation. Notably, the double vacancy defect was also a preferential site for 1O2 production. This study advances mechanistic understanding of collaborative contribution of active sites to PMS activation. 

Sulfamethoxazole degradation by regulating active sites on distilled spirits lees-derived biochar in a continuous flow fixed bed peroxymonosulfate reactor

Influence of carbon structure on performance of electrode material for electric double-layer capacitor

Effect of phosphates on oxidative species generation and sulfamethoxazole degradation in a pig manure derived biochar activated peroxymonosulfate system

Yan-su Wang

Papers

Preparation of high-performance activated carbons for electric double layer capacitors by KOH activation of mesophase pitches

Influences and mechanisms of phosphate ions onto persulfate activation and organic degradation in water treatment: A review.

Sulfamethoxazole degradation by regulating active sites on distilled spirits lees-derived biochar in a continuous flow fixed bed peroxymonosulfate reactor

Influence of carbon structure on performance of electrode material for electric double-layer capacitor

Effect of phosphates on oxidative species generation and sulfamethoxazole degradation in a pig manure derived biochar activated peroxymonosulfate system