Valorization of the inedible pistachio shells into nanoscale transition metal and nitrogen codoped carbon-based electrocatalysts for hydrogen evolution reaction and oxygen reduction reaction

Making a consistency with the objectives of circular economy, herein, waste pistachios shells were utilized for the development of hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) electrocatalysts which are the key bottleneck in the technological evolution of electrolyzers and fuel cells, respectively. As an alternative to scarce and expensive platinum-group-metal (PGM) electrocatalysts, metal nitrogen carbons (MNCs) are emerging as a promising candidate for both aforementioned electrocatalysis where iron and nickel are the metal of choice for ORR and HER, respectively. Therefore, FeNCs and NiNCs were fabricated utilizing inedible pistachio shells as a low-cost biosource of carbon. The steps involved in the fabrication of electrocatalyst were correlated with electrochemical performance in alkaline media. Encouraging onset potential of similar to 0.88 V vs RHE with a possibility of a 2 +2 reaction pathway was observed in pyrolyzed and ball-milled FeNC. However, HF etching for template removal slightly affected the kinetics and eventually resulted in a relatively higher yield of peroxide. In parallel, the pyrolyzed NiNC demonstrated a lower HER overpotential of similar to 0.4 V vs RHE at -10 mA cm(-2). Nevertheless, acid washing adversely affected the HER performance and consequently, very high overpotential was witnessed

Engineered biochar derived from pyrolyzed waste tea as a carbon support for Fe-N-C electrocatalysts for the oxygen reduction reaction

Platinum metal group (PGM-free) electrocatalysts for oxygen reduction reaction (ORR) were synthesized by ball milling of activated biochar and Fe(II) phthalocyanine. The biochar used as a carbon support was produced from pyrolysis of waste tea leaves at 1500 °C in argon atmosphere. The pyrolyzed waste tea was then activated with CO2 or urea. FE-SEM, HR-TEM, XPS, and Raman analyses were performed to investigate the morphology and the physicochemical properties of the electrocatalysts. The ORR activity and methanol tolerance of the Fe-N-C electrocatalysts were tested in rotating ring disk electrode (RRDE), showing promising results in terms mass activity, onset and half-wave potential in alkaline environment. Two different short potential cycling protocols demonstrated the high stability of these Fe-N-C electrocatalysts, especially when compared with a 20 wt. % commercial Pt/C electrocatalys

Boosting DMFC power output by adding sulfuric acid as a supporting electrolyte: Effect on cell performance equipped with platinum and platinum group metal-free cathodes

Direct methanol fuel cells (DMFCs) are promising electrochemical systems capable of producing electricity from the electrochemical oxidation of methanol and the reduction of oxygen. In this work, the effectiveness of the addition of sulfuric acid as a supporting electrolyte for methanol fuel composition was assessed. The results showed that the peak of power curve in DMFCs with Pt/C cathode electrocatalysts increased progressively from 70 mW cm−2 (0 mM of H2SO4) to 115 mW cm−2 with a concentration of 100 mM of H2SO4. These results underlined the positive effect of the addition of a supporting electrolyte in the methanol aqueous solution on the electrochemical output that was enhanced. Platinum group metal-free (PGM-free) electrocatalysts based on Fe-Nx-C type were also tested being insensitive to methanol crossover and oxidation at the cathode. DMFC with Fe–N–C cathode catalysts result in a performance of 21.5 mW cm−2. In these operating conditions, the addition of supporting electrolyte does not seem to bring excessive advantage. Short stability tests are presented and an overall assessment of the resistances within the system is also discussed

Lignin-derived bimetallic platinum group metal-free oxygen reduction reaction electrocatalysts for acid and alkaline fuel cells

Metal-nitrogen-carbons (M-N-Cs) as a reliable substitution for platinum-group-metals (PGMs) for oxygen reduction reaction (ORR) are emerging candidates to rationalize the technology of fuel cells. The development of M-N-Cs can further be economized by consuming waste biomass as an inexpensive carbon source for the electrocatalyst support. Herein, we report the simple fabrication and in-depth characterization of electrocatalysts using lignin-derived activated char. The activated char (LAC) was functionalized with metal phthalocyanine (FePc and MnPc) via atmosphere-controlled pyrolysis to produce monometallic M-N-Cs (L_Mn and L_Fe) and bimetallic M1-M2-N-Cs (L_FeMn) electrocatalysts. Raman spectroscopy and transmission electron microscopy (TEM) revealed a defect-rich architecture. XPS confirmed the coexistence of various nitrogen-containing active moieties. L_Fe and L_FeMn demonstrated appreciable ORR in both acidic and alkaline conditions whereas L_FeMn helped in restricting the peroxide yield, particularly in alkaline media. L_Fe and L_FeMn demonstrated remarkable onset potential (Eonset) of -0.942 V (vs RHE) with an E1/2 of 0.874 V (vs RHE) in 0.1 M KOH. In acid, L_FeMn had an Eonset of 0.817 V (vs RHE) and an E1/2 of -0.76 V (vs RHE). Finally, the L_FeMn as a cathode electrocatalyst was integrated and tested in PEMFC and AEMFC. AEMFC demonstrated optimistic performance with a peak power density of 261 mW cm-2 at the current density of -577 mA cm-2