Litchi-derived platinum group metal-free electrocatalysts for oxygen reduction reaction and hydrogen evolution reaction in alkaline media

Within the framework of the circular economy, the waste litchi's skins were upgraded and transformed into electrocatalysts for oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER). The waste litchi's skins were pyrolyzed, activated, and then used as carbon support for fabricating metal-nitrogen-carbons (M-N-Cs) which belong to a promising class of platinum group metal-free electrocatalysts. The activated char was functionalized with transition metal (Fe, Ni, and Co)- phthalocyanine (Pc) in monometallic and bimetallic fashion by subjecting it to a thermal treatment at 600 and 900 degrees C. The samples functionalized at 900 degrees C showed higher performance for HER due to the formation of metal nanoparticles, whereas the samples functionalized at 600 degrees C showed higher performance for ORR. Particularly, sample Ni-Co 900 had an overpotential of -0.38 V for HER, while the sample Fe 600 was the most active electrocatalyst for ORR by demonstrating the onset potential of similar to 0.9 V (a half-wave potential of similar to 0.81 V) with the least production of unwanted peroxide anion.