Oxygen Reduction Reaction Electrocatalysts Derived from Iron Salt and Benzimidazole and Aminobenzimidazole Precursors and Their Application in Microbial Fuel Cell Cathodes.

In this work, benzimidazole (BZIM) and aminobenzimidazole (ABZIM) were used as organic-rich in nitrogen precursors during the synthesis of iron-nitrogen-carbon (Fe-N-C) based catalysts by sacrificial support method (SSM) technique. The catalysts obtained, denoted Fe-ABZIM and Fe-BZIM, were characterized morphologically and chemically through SEM, TEM, and XPS. Moreover, these catalysts were initially tested in rotating ring disk electrode (RRDE) configuration, resulting in similar high electrocatalytic activity toward oxygen reduction reaction (ORR) having low hydrogen peroxide generated (<3%). The ORR performance was significantly higher compared to activated carbon (AC) that was the control. The catalysts were then integrated into air-breathing (AB) and gas diffusion layer (GDL) cathode electrode and tested in operating microbial fuel cells (MFCs). The presence of Fe-N-C catalysts boosted the power output compared to AC cathode MFC. The AB-type cathode outperformed the GDL type cathode probably because of reduced catalyst layer flooding. The highest performance obtained in this work was 162 ± 3 µWcm-2. Fe-ABZIM and Fe-BZIM had similar performance when incorporated to the same type of cathode configuration. Long-term operations show a decrease up to 50% of the performance in two months operations. Despite the power output decrease, the Fe-BZIM/Fe-ABZIM catalysts gave a significant advantage in fuel cell performance compared to the bare AC.

Influence of platinum group metal-free catalyst synthesis on microbial fuel cell performance.

Platinum group metal-free (PGM-free) ORR catalysts from the Fe-N-C family were synthesized using sacrificial support method (SSM) technique. Six experimental steps were used during the synthesis: 1) mixing the precursor, the metal salt, and the silica template; 2) first pyrolysis in hydrogen rich atmosphere; 3) ball milling; 4) etching the silica template using harsh acids environment; 5) the second pyrolysis in ammonia rich atmosphere; 6) final ball milling. Three independent batches were fabricated following the same procedure. The effect of each synthetic parameters on the surface chemistry and the electrocatalytic performance in neutral media was studied. Rotating ring disk electrode (RRDE) experiment showed an increase in half wave potential and limiting current after the pyrolysis steps. The additional improvement was observed after etching and performing the second pyrolysis. A similar trend was seen in microbial fuel cells (MFCs), in which the power output increased from 167 ± 2 µW cm-2 to 214 ± 5 µW cm-2. X-ray Photoelectron Spectroscopy (XPS) was used to evaluate surface chemistry of catalysts obtained after each synthetic step. The changes in chemical composition were directly correlated with the improvements in performance. We report outstanding reproducibility in both composition and performance among the three different batches.

Design of Iron(II) Phthalocyanine-Derived Oxygen Reduction Electrocatalysts for High-Power-Density Microbial Fuel Cells.

Iron(II) phthalocyanine (FePc) deposited onto two different carbonaceous supports was synthesized through an unconventional pyrolysis-free method. The obtained materials were studied in the oxygen reduction reaction (ORR) in neutral media through incorporation in an air-breathing cathode structure and tested in an operating microbial fuel cell (MFC) configuration. Rotating ring disk electrode (RRDE) analysis revealed high performances of the Fe-based catalysts compared with that of activated carbon (AC). The FePc supported on Black-Pearl carbon black [Fe-BP(N)] exhibits the highest performance in terms of its more positive onset potential, positive shift of the half-wave potential, and higher limiting current as well as the highest power density in the operating MFC of (243±7) µW cm-2 , which was 33 % higher than that of FePc supported on nitrogen-doped carbon nanotubes (Fe-CNT(N); 182±5 µW cm-2 ). The power density generated by Fe-BP(N) was 92 % higher than that of the MFC utilizing AC; therefore, the utilization of platinum group metal-free catalysts can boost the performances of MFCs significantly.

A family of Fe-N-C oxygen reduction electrocatalysts for microbial fuel cell (MFC) application: Relationships between surface chemistry and performances.

Different iron-based cathode catalysts have been studied for oxygen reduction reaction (ORR) in neutral media and then applied into microbial fuel cells (MFC). The catalysts have been synthesized using sacrificial support method (SSM) using eight different organic precursors named Niclosamide, Ricobendazole, Guanosine, Succinylsulfathiazole, Sulfacetamide, Quinine, Sulfadiazine and Pyrazinamide. Linear Sweep Voltammetry (LSV) curves were obtained for the catalysts using a O2 saturated in 0.1 M potassium phosphate buffer and 0.1 M KCl solution and a Rotating Ring Disk Electrode (RRDE) setup in order to study the ORR characteristics. Additionally, we analyze the peroxide yield obtained for each catalyst which helps us determine the reaction kinetics. Those catalysts have been mixed with activated carbon (AC), carbon black (CB) and PTFE and pressed on a metallic mesh forming a pellet-like gas diffusion electrode (GDE). Results showed that Fe-Ricobendazole, Fe-Niclosamide and Fe-Pyrazinamide had the highest cathode polarization curves and highest power densities output that was above 200 µWcm-2. Fe-Ricobendazole, Fe-Niclosamide, Fe-Pyrazinamide, Fe-Guanosine Fe-Succinylsulfathiazole and Fe-Sulfacetamide outperformed compared to Pt cathode. Fe-Sulfadiazene and Fe-Quinine performed better than AC used as control but less than Pt. Correlation of surface composition with performance showed that power density achieved is directly related to the total amount of nitrogen, and in particularly, N coordinated to metal and pyridinic and pyrrolic types while larger amounts of graphitic nitrogen result in worse performance.

Large scale synthesis of graphene quantum dots (GQDs) from waste biomass and their use as an efficient and selective photoluminescence on-off-on probe for Ag(+) ions.

Graphene quantum dots (GQDs) are synthesized from bio-waste and are further modified to produce amine-terminated GQDs (Am-GQDs) which have higher dispersibility and photoluminescence intensity than those of GQDs. A strong fluorescence quenching of Am-GQDs (switch-off) is observed for a number of metal ions, but only for the Ag(+) ions is the original fluorescence regenerated (switch-on) upon addition of L-cysteine.

Synthesis of an efficient heteroatom-doped carbon electro-catalyst for oxygen reduction reaction by pyrolysis of protein-rich pulse flour cooked with SiO2 nanoparticles.

Development of a highly durable, fuel-tolerant, metal-free electro-catalyst for oxygen reduction reaction (ORR) is essential for robust and cost-effective Anion Exchange Membrane Fuel Cells (AEMFCs). Herein, we report the development of a nitrogen-doped (N-doped) hierarchically porous carbon-based efficient ORR electrocatalyst from protein-rich pulses. The process involves 3D silica nanoparticle templating of the pulse flour(s) followed by their double pyrolysis. The detailed experiments are performed on gram flour (derived from chickpeas) without any in situ/ex situ addition of dopants. The N-doped porous carbon thus generated shows remarkable electrocatalytic activity towards ORR in the alkaline medium. The oxygen reduction on this material follows the desired 4-electron transfer mechanism involving the direct reduction pathway. Additionally, the synthesized carbon catalyst also exhibits good electrochemical stability and fuel tolerance. The results are also obtained and compared with the case of soybean flour having higher nitrogen content to highlight the significance of different parameters in the ORR catalyst performance.

Laser synthesized super-hydrophobic conducting carbon with broccoli-type morphology as a counter-electrode for dye sensitized solar cells.

A laser photochemical process is introduced to realize superhydrophobic conducting carbon coatings with broccoli-type hierarchical morphology for use as a metal-free counter electrode in a dye sensitized solar cell. The process involves pulsed excimer laser irradiation of a thin layer of liquid haloaromatic organic solvent o-dichlorobenzene (DCB). The coating reflects a carbon nanoparticle-self assembled and process-controlled morphology that yields solar to electric power conversion efficiency of 5.1% as opposed to 6.2% obtained with the conventional Pt-based electrode.