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In this work a first approximation to obtain non-noble metal electrocatalysts from onion skin wastes is reported. Biocarbon were obtained at a range of 600–800 °C of pyrolysis temperature activated by chemical treatment with HNO3. It was observed that the pyrolysis temperature has a direct effect on the structural and textural properties, besides the morphology of the onion skin waste-derived biocarbon, which shows to have influence on the catalytic activity for the oxygen reduction reaction ORR. AOB700 was the non-noble metal electrocatalyst with the best performance for the ORR evaluated in alkaline electrolyte (0.5 mol L−1 KOH), which had the highest surface area (242 m2g-1) and a current density of −2.35 mA cm−2 with an onset potential of 0.82 V/RHE. The chemical surface composition shows that N-pyridinic, N-amine, N-quaternary and N-pyrrolic nitrogen species are present on this electrocatalysts. The use of onion skin waste as raw material in the production of non-noble metal electrocatalysts is a sustainable solution to avoid the disposal of abundant biomass residues as onion skins.

In this work, high surface area N-doped carbon synthesis from Sargassum spp. is reported as a low cost alternative for electrocatalysts production for the oxygen reduction reaction (ORR). First, Sargassum spp. was activated with potassium hydroxide (SKPH) and then doped with hydrazine (SKPHD). As a result of the activation process, SKPH obtained a high surface area (2289 m2 g−1), 0.16% nitrogen and 2.63% sulfur content; it also showed four-electron-transfer mechanism when tested as electrocatalyst in alkaline medium. Besides, SKPHD presented 3.60% nitrogen content in the bulk and higher ORR activity (0.838 V onset potential vs. RHE and 4.59 mA cm−2 current density) very close to 20% Pt/C (5.25 mA cm−2). Results indicate that using seaweeds as a synthesis precursor is an alternative for the Sargassum spp. disposal in the Caribbean due to its high availability and efficiency towards ORR.

Metal-free electrocatalysts for the oxygen reduction reaction (ORR) were synthesized from cassava residues through a thermal functionalization with sulfuric acid. Their electrocatalytic activities were tested through the ORR performance in basic media. Chemical composition in samples seems to play an important role in their electroactivity, more than textural properties, as the sulfur-treated high-temperature sample (Sy800) has the best performance with an onset potential of 0.69 V vs RHE (reversible hydrogen electrode) and a current of −2.32 mA cm−2 at 0.3 V vs RHE. These functionalized cassava residues are promising materials to be used like carbon-based metal-free electrocatalysts.

In this work, the synthesis and characterization of novel metal-free electrocatalysts obtained from leather scraps is reported. The waste material has been subjected to simple thermochemical treatments (pyrolysis, chemical activation and doping), obtaining high performance electrocatalysts for the Oxygen Reduction Reaction (ORR) in KOH. The effect of pyrolysis temperature on the physicochemical properties and electrochemical performance is studied. The metal-free electrocatalysts possess mesoporous structure with high specific surface area (819–2100 m 2 g −1 ). A higher catalytic activity has been determined for the electrocatalyst treated at 700 °C (AB7), compared to samples pyrolyzed at higher temperatures. Furthermore, AB7 delivers a higher current density compared with commercial 20% Pt/C (j = 9.0 and 4.5 mA cm −2 , respectively), while its on-set potential shifts only 145 mV to more negative values. The metal-free catalysts are a promising eco-friendly and scalable alternative as cathode materials for alkaline fuel cells and other electrochemical energy devices.