This Ph.D. thesis addresses the challenging goal of integrating supercapacitive features in MFCs by sustainable materials and processes and valorizing wastes by their processing as key components of supercapacitors and MFCs. Three main research lines have been pursued: i) the development of green supercapacitors by exploiting natural polymers as binders and electrospun separators, ii) the improvement of the power output of MFCs by the external integration of commercial and green supercapacitors, and ii) the development of supercapacitive microbial fuel cells by the monolithic integration of supercapacitive features in MFCs. This Thesis is articulated in the following Sections. Chapter 1 introduce the energy-water nexus, highlights the role played by supercapacitors and MFCs in this context, and describes the main components, and processes in these devices.