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.
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•Use as onion skin waste as potential raw material in the synthesis of as non-noble metal electrocatalysts for the ORR.•Effect of the pyrolysis temperature on the catalytic activity of onion skin-derived biocarbon towards ORR.•N-doped biocarbon as non-noble metal electrocatalyst for alkaline low temperature fuel cells.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
This study presents a green method of producing copper nanoparticles (CuNPs) using aqueous extracts from Sargassum spp. as reducing, stabilizing, and capping agents. The CuNPs created using this ...algae‐based method are not hazardous, they are eco‐friendly, and less toxic than their chemically synthesized counterparts. The XRD characterization of the CuNPs revealed the presence of Cu and CuO, with a crystallite size ranging from 13 to 17 nm. Following this, the CuNPs were supported onto a carbon substrate, also derived from Sargassum spp. (biochar CSKPH). The CuNPs in biochar (CuNPs‐CSKPH) did not appear in the XRD diffractograms, but the SEM‐EDS results showed that they accounted for 36 % of the copper weight. The voltamperometric study of CuNps‐CSKPH in acid media validated the presence of Cu and the amount was determined to be 2.58 μg. The catalytic activity of CuNPs‐CSKPH was analyzed for the electrochemical reduction of CO2. The use of Sargassum spp. has great potential to tackle two environmental problems simultaneously, by using it as raw material for the synthesis of activated biochar as support, as well as the synthesis of CuNPs, and secondly, by using it as a sustainable material for the electrochemical conversion of CO2.
CuNPs were synthesized using a cost‐effective and environmentally friendly extract applying Sargassum spp. as versatile reducing agent. In this study, CuNPs with nanoflower morphology were synthesized. The experimental characterizations (XRD, SEM, and TEM,) recommend that the green synthesis method has promising effect for the synthesis of CuNPs, stable and homogeneously dispersed onto biochar. The CuNPs‐CSKPH is promising electrocatalyst for the electrochemical reduction of CO2.
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FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK
In this work, we have developed metal-free electrocatalysts based on sulfur and/or nitrogen-doped carbon nanofibers (CNFs) by in situ electrospun doping method. Heteroatom-doped CNFs have diameter ≈ ...350 nm and nitrogen and sulfur species on their surface. Moreover, the catalytic activity for the oxygen reduction reaction (ORR) is evaluated in alkaline electrolyte (0.5M KOH). The most active metal-free electrocatalyst labelled as S-CNF has an onset potential of 0.817 V vs. RHE, HO
2
-
% yield of ≈12-15% and n = 3.7 and high ethanol tolerance. The Accelerated Degradation Test (ADT) show that S-CNF catalytic activity decrease only 13% evaluated at a potential range of 0.6 to 1.0 V vs. RHE. Furthermore, S-CNF even is evaluated by ADT as support (1.0 to 1.6 V/RHE, 6000 cycles) showing high long-term stability decreasing only 11% its catalytic activity. These results indicate N-S-codoped CNFs are a promising and eco-friendly alternative for fuel cells applications.
We report a novel process to synthesize graphene (G) catalyst by mechanical milling using graphite flakes as the precursor. G sample has been doped ex situ with hydrazine as nitrogen source via ...solvothermal procedure to obtain the GD1 catalyst. In a second approach, the GD2 sample has been synthesized doping G with uric acid as nitrogen precursor in situ, i.e., during the milling step. Doping with nitrogen increases the ID/IG Raman spectra ratios of GD1 and GD2 to 1.52 and 1.12, respectively, higher than 1.02 of G. XPS analysis shows that Pyridinic, Amine, Pyrrolic, Graphitic and Oxidized nitrogen are formed at GD1, while only Pyrrolic is present at GD2. Evaluation of catalytic activity for the ORR in 0.5 mol L−1 KOH shows an increase in onset potential (Eonset) of the ORR at GD1, compared to G and GD2. GD1 also generated a higher current density (j) at 0.83 V than G and GD2. The results show that mechanical milling is an efficient method to synthesize G. Even though, the doping can still be improved to form more Nitrogen that promotes the ORR, specifically Pyridinic N and Graphitic N.
•Large-scale and low cost production of N-doped graphene by mechanical milling with ORR activity.•Two methods of doping graphene and their influence in the generated NC bonds.•N-doped graphene as metal-free electrocatalyst for alkaline low temperature fuel cells.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
In this work, electroactive biofilms of Bacillus subtilis (B. subtilis) or Escherichia coli (E. coli) were supported on functionalized biocarbon (AB7-F), which was synthesized from waste leather and ...was used as catalysts to develop bioanodes for microbial fuel cells (MFCs). This way, bioanodes were fabricated and further evaluated in a three-electrode cell using pharmaceutical wastewater (PWW) as substrate. The electrochemical measurements showed a higher performance of the bioanode based on AB7-f+ B. subtilis to oxidize organic matter from PWW. The polarization curves in the dual-chamber MFC showed that AB7-f+ B. subtilis bioanode can generate an open circuit voltage of 602 mV and a power density of 77 mW m−2. During long-term tests of the MFC, a variation in performance was observed, with a maximum of 96.3 mW m−2 on day 7. Such variation was attributed to the development of more stable biofilm as well as consumption of some compounds metabolized by bacteria grown on the bioanode. The results showed that AB7-f+ B. subtilis can be used as bioanode for MFCs with PWW as substrate removing around 45% of the chemical oxygen demand (COD).
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FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK
Different chemical and physical treatments have been used to improve the properties and functionalities of steels. Anodizing is one of the most promising treatments, due to its versatility and easy ...industrial implementation. It allows the growth of nanoestructured oxide films with interesting properties able to be employed in different industrial sectors. The present work studies the influence of the anodizing time (15, 30, 45 and 60 min), as well as the stirring speed (0, 200, 400, and 600 rpm), on the morphology and the corrosion resistance of the anodic layers grown in 304L stainless steel. The anodic layers were characterized morphologically, compositionally, and electrochemically, in order to determine the influence of the anodization parameters on their corrosion behavior in a 0.6 mol L−1 NaCl solution. The results show that at 45 and 60 min anodizing times, the formation of two microstructures is favored, associated with the collapse of the nanoporous structures at the metal-oxide interphace. However, both the stirring speed and the anodizing time have a negligeable effect on the corrosion behavior of the anodized 304L SS samples, since their electrochemical values are similar to those of the non-anodized ones.
The catalytic activity and electrochemical stability of Pd‐CeO2‐NR/C (CeO2‐NR: cerium oxide nanorods) for the Oxygen Reduction Reaction (ORR) and the Ethanol Oxidation Reaction (EOR) is shown in ...alkaline media and compared to Pd/C. Evaluation of catalytic activity for the ORR in a Rotating Ring Disc Electrode (RRDE) set‐up, shows that Pd‐CeO2‐NR/C promotes the reaction with a percentage of hydrogen peroxide production (%H2O2) around 2–4 %, and an electron transfer number (n) close to 4. Tafel plots demonstrates higher mass and specific activities of Pd‐CeO2‐NR/C than Pd/C. Moreover, from cyclic voltammetry tests, Pd‐CeO2‐NR/C shows a higher mass catalytic activity (jm= 697 mA mg−1Pd) for the EOR at a more negative onset potential (Eonset= 0.29 V/RHE) than Pd/C. After Accelerated Degradation Tests (ADT), Pd‐CeO2‐NR/C retains ∼98 % of its Electrochemically Active Surface Area (ECSA), higher than ∼51 % of Pd/C. After ADT, the performance of Pd‐CeO2‐NR/C remains similar for the ORR, while it is significantly higher for the EOR, compared to Pd/C. Thus, the addition of CeO2‐NR enhances the electrocatalytic behavior and stability of Pd towards the ORR and the EOR.
Pd‐CeO2‐NR/C (CeO2‐NR=cerium oxide nanorods) is a novel bifunctional nanocatalyst with application as anode for the Ethanol Oxidation Reaction (EOR) and as cathode for the Oxygen Reduction Reaction (ORR). It shows a high mass and specific catalytic activity for the ORR and excellent performance for the EOR (63 % increase in jm after ADT), along with remarkable electrochemical stability (98 % of ECSA retention) after ADT.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
In the past few decades, nanostructured carbons (NCs) have been investigated for their interesting properties, which are attractive for a wide range of applications in electronic devices, energy ...systems, sensors, and support materials. One approach to improving the properties of NCs is to dope them with various heteroatoms. This work describes the synthesis and study of sulfur-added carbon nanohorns (S-CNH). Synthesis of S-CNH was carried out by modified chemical vapor deposition (m-CVD) using toluene and thiophene as carbon and sulfur sources, respectively. Some parameters such as the temperature of synthesis and carrier gas flow rates were modified to determine their effect on the properties of S-CNH. High-resolution scanning and transmission electron microscopy analysis showed the presence of hollow horn-type carbon nanostructures with lengths between 1 to 3 µm and, diameters that are in the range of 50 to 200 nm. Two types of carbon layers were observed, with rough outer layers and smooth inner layers. The surface textural properties are attributed to the defects induced by the sulfur intercalated into the lattice or bonded with the carbon. The XRD patterns and X-ray microanalysis studies show that iron serves as the seed for carbon nanohorn growth and iron sulfide is formed during synthesis.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
In this study, metal-free electrocatalysts were obtained from the pyrolysis of commercial Kevlar™ and Twaron™ carbon fibers (pKf and pTf, respectively). An easy and low cost synthesis method was ...developed. The obtained electrocatalysts have a significantly lower cost than conventional platinum based electrocatalysts. Synthesis of the electrocatalyst was made by pyrolysis treatment of the carbon fibers, under nitrogen atmosphere, followed by an activation treatment under carbon dioxide atmosphere. Properties and electrochemical performance of pyrolyzed (pKf, pTf) and activated (aKf and aTf) samples were compared. The electrocatalysts obtained have surface areas of up to 1000 m2/g after the activation treatment. Morphology and structural characteristics were studied by Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), Raman Spectroscopy and X-ray photoelectron spectroscopy (XPS). The electroactivity of these electrocatalysts was evaluated by the oxygen reduction reaction (ORR) in acid media by rotating disk electrode technique. Carbon fibers showed an improvement in the ORR after receiving the activation treatment.
•Nitrogen-doped metal-free electrocatalysts synthesized from polymer fibers (aramids).•Carbon fibers synthesized from commercial Kevlar™ and Twaron™.•Activation process of the pyrolyzed fibers carried out in a CO2 atmosphere.•High surface areas with nitrogen content in activated fibers.•Nitrogen-doped electrocatalysts evaluated for ORR in acid media.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The development of numerous biomass-derived carbon catalysis toward the oxygen reduction reaction (ORR) have been reported in the last decade. The catalytic activity for the ORR improves with ...heteroatom doping and is notably high when Fe-N-C type bonds are present. In this work, we developed a novel method to obtain Fe-N-C self-doped sewage sludge-derived biocarbons (SSBs) by intermittent microwave heating (IMH) technique. The effect of IMH on the structural and textural properties of SSBs, and their correlation with the catalytic activity for ORR was studied. The most active biocarbon was labeled as SSF, which was obtained by two-step process: chemical activation using KOH and then it was functionalized with methanol by IMH. Therefore, the obtained SSF micro-mesoporous biocarbon had high surface area (1127 m
2
g
-1
) and quaternary-N and thiophene-S species. In addition, Fe-N-C bonds were detected on the surface of SSF. On the other hand, it was observed that IMH treatment improved the electrochemical parameters such as the on-set potential (E
0
), current density (j), electron transfer number (n) and %HO
2
-
production. In this regard, SSF shows the best performance toward the ORR (E
0
= 0.89 V vs RHE, j= -3.01 mA cm
-2
, n= 3.4 and %HO
2
-
= 25.85). These results indicate that sewage sludge could be used as raw material for the manufacture of cathodes, and that the treatment by IMH seems a promising eco-friendly alternative.
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