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

Abstract

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 ~ 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 ~ 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.

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

“…For the execution of electrochemical studies, first, a conductive ink of the electrocatalyst was prepared similar to our previously reported methods [39,40]. In brief, 5 mg of the electrocatalyst was mixed with a solvent containing 985 μl of isopropanol (Alfa Aesar) and 15 μl of 5.0 wt.% Nafion® D-520 (Alfa Aesar).…”

Litchi‐derived platinum group metal‐free electrocatalysts for oxygen reduction reaction and hydrogen evolution reaction in alkaline media

“…[53][54][55][56] Where the graphitization is considered favorable for the electron transfer during electrocatalysis, defects and discontinuities within carbonaceous structure act as electro-catalytically active moieties for ORR and can also contribute to HER. 25,39,57,58,59,60 The intensity ratio I D /I G of the D and G band is widely used for characterizing the defect quantity in graphitic materials.…”

“…Recently, researches report the advancements done in this direction for the synthesis of HER and ORR electrocatalysts. 24,39,40 Different sorts of biochar have been made from different wastes, such as algae, pistachio waste, and tea waste. 39,41,42 Generally, biochars have chemical stability, optimum electrical conductivity, and considerable mass transportability.…”

“…24,39,40 Different sorts of biochar have been made from different wastes, such as algae, pistachio waste, and tea waste. 39,41,42 Generally, biochars have chemical stability, optimum electrical conductivity, and considerable mass transportability. Moreover, due to their large surface area and good conductivity, they show high-power charge-discharge potential and high reversible capacity.…”

Waste-Derived Catalysts for Water Electrolysis: Circular Economy-Driven Sustainable Green Hydrogen Energy

“…Specifically, S dopants can lead to significant changes in the electronic structures and enhance the adsorption of the H atom intermediate on catalysts, which could improve the HER activity more efficiently than single N doping [110]. Besides nonmetal doping, transitional metals also have been incorporated into carbon materials, such as Zn, S, N self-doped carbon [111], Co, N co-doped carbon [112], Ni, N co-doped carbon [113,114], and N, P, Ca co-doped biochar [115]. The presence of metal atoms can significantly improve catalytic performance by increasing the electrical conductivity and taking the advantage of synergistic effects of different elements [115].…”