Dual-Template Pore Engineering of Whey Powder-Derived Carbon as an Efficient Oxygen Reduction Reaction Electrocatalyst for Primary Zinc-Air Battery.

Cost-effective and high-performance electrocatalysts for oxygen reduction reactions (ORR) are needed for many energy storage and conversion devices. Here, we demonstrate that whey powder, a major by-product in the dairy industry, can be used as a sustainable precursor to produce heteroatom doped carbon electrocatalysts for ORR. Rich N and S compounds in whey powders can generate abundant catalytic active sites. However, these sites are not easily accessible by reactants of ORR. A dual-template method was used to create a hierarchically and interconnected porous structure with micropores created by ZnCl2 and large mesopores generated by fumed SiO2 particles. At the optimum mass ratio of whey power: ZnCl2  : SiO2 at 1 : 3 : 0.8, the resulting carbon material has a large specific surface area close to 2000 m2  g-1 , containing 4.6 at.% of N with 39.7% as pyridinic N. This carbon material shows superior electrocatalytic activity for ORR, with an electron transfer number of 3.88 and a large kinetic limiting current density of 45.40 mA cm-2 . They were employed as ORR catalysts to assemble primary zinc-air batteries, which deliver a power density of 84.1 mW cm-2 and a specific capacity of 779.5 mAh g-1 , outperforming batteries constructed using a commercial Pt/C catalyst. Our findings open new opportunities to use an abundant biomaterial, whey powder, to create high-value-added carbon electrocatalysts for emerging energy applications.