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Fe-Nx-C electrocatalysts for the oxygen reduction reaction are typically fabricated via pyrolysis. However, the pyrolysis process is poorly understood. Therefore, a systematic investigation was initiated to elucidate the effects of the pyrolysis conditions (atmosphere and temperature) on the evolution of active sites starting from iron phthalocyanine supported over carbon black. The atomic level dispersion of Fe-Nx is sustained up to 600 °C and afterward, the growth of iron oxide nanoparticles is observed. Interestingly, the different X-ray absorption spectroscopy fingerprints acquired during in-situ and ex-situ experiments indicated the bonding of oxygen as a fifth ligand on the Fe sites when exposed to the open air. The ORR activities were analyzed in acidic and alkaline media. The best electrocatalytic activity was observed for the electrocatalysts pyrolyzed at 600 °C. Above this temperature, a reduction in the activity was observed. Surface-to-reactivity analysis was carried out identifying the relationship between surface chemistry/morphology and electrocatalytic activity.

In this manuscript, a comprehensive study is presented on Fe-based electrocatalysts with mono, bi, and tri-metallic compositions, emphasizing the influence of processing-structure correlations on the electrocatalytic activity for the oxygen reduction reaction (ORR) in the alkaline medium. These electrocatalysts were synthesized through the mixing of transition metal phthalocyanines (TM-Pc) with conductive carbon support, followed by controlled thermal treatment at specific temperatures (600 °C and 900 °C). An extensive analysis was conducted, employing various techniques, including X-ray Absorption Spectroscopy (XAS), Transmission Electron Microscopy (TEM), and X-ray Diffraction (XRD), providing valuable insights into the structural characteristics of the synthesized nanoparticles. Importantly, an increase in the Fe-Pc weight percentage from 10% to 30% enhanced the ORR activity, although not proportionally. Furthermore, a comparative analysis between mono, bi, and tri-metallic samples subjected to different functionalization temperatures highlighted the superior electrocatalytic activity of electrocatalysts functionalized at 600 °C, particularly Fe 600 and Fe-Ni-Cu 600. These electrocatalysts featured Eon values of 0.96 V vs. RHE and E1/2 values of 0.9 V vs. RHE, with the added benefit of reduced anionic peroxide production. The potential of these Fe-based electrocatalysts to enhance ORR efficiency is underscored by this research, contributing to the development of more effective and sustainable electrocatalysts for energy conversion technologies.

In this work, platinum group metal-free (PGM-free) electrocatalysts were synthesized, characterized, and tested for hydrogen evolution reaction (HER). These materials were mono-, bi- and trimetallic Ni-based electrocatalysts with the addition of a second or a third transition metal (TM), such as iron and cobalt. TM–phthalocyanine (TMPc) was used as a metal precursor, mixed with a conductive carbon backbone and subjected to pyrolysis under controlled temperature and atmosphere conditions. Two temperatures of pyrolysis (600 °C and 900 °C) were used. The effect of TM loading in the precursors, different pyrolysis temperatures on the surface chemistry and morphology, and electrocatalytic activity towards HER were evaluated. The increase of NiPc in the initial mixture is beneficial to improving the electrocatalytic activity. The addition of a second and a third metal reflects positively on the HER performance. Interestingly, the pyrolysis temperature influences both the formation and growth of the nanoparticles, and this information is supported by high-resolution transmission electron microscopy (HR-TEM) and light synchrotron X-ray absorption spectroscopy (XAS) measurements.

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°C. The samples functionalized at 900°C showed higher performance for HER due to the formation of metal nanoparticles, whereas the samples functionalized at 600°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 ∼0.9 V (a half-wave potential of ∼0.81 V) with the least production of unwanted peroxide anion.

Getting inspiration from the ‘waste to resource’ strategic theme of circular economy, herein, we present the upcycling of the critical raw material i.e. Co-containing waste cathode from spent lithium-ion batteries (LIBs) into platinum group metal-free (PGM-free) electrocatalysts for hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR). Lithium cobalt oxide-based cathode was recovered from spent LIBs (Waste LCOd) and subsequently treated with choline chloride: citric acid 1:1 deep eutectic solvent (DES) to obtain the full degradation of the LCO-type structure and, post thermal treatments, cobalt oxide in a carbonaceous matrix (ChCl.Citric). HER and ORR activities of derived materials were investigated in alkaline media using the rotating disk electrode (RDE) and rotating ring disk electrode (RRDE), respectively. To elucidate the role of cobalt present in the derived electrocatalysts, inks were prepared by supporting the electrocatalysts with different proportions of Ketjenblack (10:90 and 50:50 ratios). Waste LCOd closely followed the electrochemical response of commercial LCO and demonstrated the least overpotential (277 mV at −10 mA cm−2) for HER with an electrode configuration of 50:50. Whereas, ChCl.Citric 50:50 outperformed the other counterparts for ORR and exhibited a remarkable onset potential of 0.85 V (vs RHE) with the least peroxide production.