Investigation of Co3O4 modified carbon black as an efficient non-noble metal oxygen reduction catalyst in self-driven phosphorus recovery systems

Abstract

Phosphorus and nitrogen recovery from urine in the form of struvite via a Mg-air fuel cell (MAFC) platform has previously been reported as a promising approach to achieving sustainable development goals. However, the applicability of this technology has been hindered by the expensive cathodic catalyst, i.e., Pt/C. In this study, an efficient and cost-effective non-precious metal catalyst, the Co3O4 doped carbon black (CB-ZIF-900), was developed to maximize nitrogen and phosphate recovery from urine while reducing investment costs. CB-ZIF-900 exhibited an oxygen reduction reaction current density of 2.95 mA cm−2 and an electron transfer number between 3.7 and 3.9 in urine solution, which approached those of commercial Pt/C at the same testing conditions. Using the MAFC, over 99 % of phosphorus was removed from urine, and >95 % of phosphorus was recovered in the precipitates. Stable phosphorus removal efficiency and precipitates composition were observed over five consecutive batch experiments. Furthermore, the MAFC with CB-ZIF-900 exhibited a maximum power density of 594.89 W m−3, surpassing that with commercial Pt/C by 9.3 %. These findings underscore the utility of the highly efficient and cost-effective CB-ZIF-900 for advancing the scalability and widespread applications of self-driven phosphorus recovery systems.