Bovine blood husbandry waste as a pathway to renewable energy

Abstract By virtue of their large surface area, extensive charge delocalization, good conductivity, and high mass transfer efficiency, heteroatom-doped hierarchically porous carbons are ideal micro/nano reactors or catalysts for various electrochemical processes. Bovine blood plasma, a major by-product of the food industry, contains abundant organic–inorganic composites (e.g., bovine serum albumin and NaCl). We have prepared several biocarbons with different doping states and porosities by pyrolysis of the organic–inorganic aggregates in blood plasma in the presence of alkali or alkaline earth metal (AM) salts. In the case of AM = Ca, synergistic effects associated with molten NaCl etching and pyrolysis-generated CaO/CaClOH templates lead to porous carbons (denoted as PC-Ca/Na) having multimodal pores and high nitrogen concentrations. As a result, PC-Ca/Na proves to be an excellent carbon-based metal-free electrocatalyst with a remarkable positive half-wave potential of 0.88 V, and a negative shift of only 3 mV after 10,000 potential cycles. Zn–air batteries fabricated by using PC-Ca/Na exhibit a peak power density of 152 mW cm–2 at a current density of 242 mA cm−2, outperforming a benchmark Pt/C catalyst. The multimodal-pore formation strategy developed in this work offers an effective approach to make full use of biowaste to fabricate high-performance device materials.