Upcycling of cattle manure for simultaneous energy recovery and supercapacitor electrode production

Organic waste, such as cattle manure, is a serious matter of concern because of its disruptive impact on the environment. Even though disposal and reclaim of cattle manure represent the first lines of intervention to solve this problem, upcycling strategies should eventually be essential to reconvert huge amounts of the waste. In the present study, a pyrolysis process was used to reclaim value from cattle manure. Through the process, cattle manure was transformed into pyrolytic gas, pyrolytic liquid, and porous carbon material. The porous carbon material was further carbonized followed by an activation step to make a supercapacitor electrode. The electrode of a hierarchical porous carbon (termed as CMPC) is formed via carbonization and activation processes of solid residue derived from the pyrolysis of cattle manure. The bicontinuous structure of CMPC provide good ion and electron transport pathways, enabling fast charge-discharge. Specifically, in a basic solution electrolyte, CMPC electrode exhibits significant specific capacitance of 161 F g−1 at 0.4 A g−1, comparable to or even larger than other biomass-derived carbon electrodes, and high rate-performance (62% of low-capacitance). It also shows long cycle lives for at least 10,000 charge-discharge cycles at a constant current of 2.7 A g−1. As the pyrolytic gas and pyrolytic liquid had higher heating values of 7.6 MJ kg−1 and 8 MJ kg−1, respectively, they can potentially be used as fuels to supply heat and energy to the pyrolysis process. The cattle manure upcycling process could greatly contribute to the reduction in greenhouse gas emissions.