Hierarchical porous carbon for high-performance capacitor derived from sewage sludge by KHCO3 activation

Porous carbon obtained by activating sewage sludge char is shown to be a viable supercapacitor electrode material. When utilizing typical activation agents like KOH, however, its electrochemical performance is hampered by high ash content from sludge and a paucity of mesopores. In this work, the production of hierarchical porous carbon from high-ash sewage sludge pyrochar is demonstrated using a novel activation method. The removal of ash was assisted by HF washing, whereas the extension of mesopores was aided by KHCO3. The carbon generated after washing with HF and HCl had an excellent electrochemical performance, with a specific capacitance of 287 F/g at 1A/g and 235 F/g at 10A/g. At 10000 times, the capacitance retention was greater than 93%. Furthermore, several carbonization processes and washing procedures were examined. The results showed that, compared to pyrochar, the carbon from hydrochar had a low surface area and poor capacitor performance due to the less formed micropores. Because of the significant ash concentration, the voltage window of the pyrochar capacitor was relatively limited without HF washing.

Automated summary

By using a novel activation method, hierarchical porous carbon can be produced from high-ash sewage sludge char, which demonstrates excellent electrochemical performance. HF washing for ash removal and KHCO3 for mesopores extension are crucial steps.