Understanding, measuring and tuning the electrochemical properties of biochar for environmental applications

Biochar, the solid carbon product from the pyrolysis of biomass, has been gaining attention due to its many possible applications such as soil amendment and water or air purification. Several effects have been observed when biochar is applied to soil, including reduced greenhouse gas emissions, contaminant degradation and increased microbial activity. Recently, it has been demonstrated that some of these effects are a direct consequence of its electrochemical properties. Understanding the mechanisms that allow biochar to store and transfer electrons is essential to obtain a complete view on its role in biogeochemical redox reactions. This paper reviews the current knowledge on the electrochemical properties of biochar as well as the different techniques available to measure and modify these properties. Specific conditions (different feedstocks, additives, pyrolysis conditions) and treatments that influence biochar's electrochemical properties are also discussed, with the aim of developing biochars with enhanced electrochemical properties for specific environmental applications.