Template-Assisted Mechanosynthesis Leading to Benchmark Energy Efficiency and Sustainability in the Production of Bifunctional Fe–N–C Electrocatalysts

Abstract

Efficient and sustainable synthesis of performant metal/nitrogen-doped carbon (M–N–C) catalysts for oxygen reduction and evolution reactions (ORR/OER) is vital for the global switch to green energy technologies–fuel cells and metal–air batteries. This study reports a solid-phase template-assisted mechanosynthesis of Fe–N–C, featuring low-cost and sustainable FeCl3, 2,4,6-tri­(2-pyridyl)-1,3,5-triazine (TPTZ), and NaCl. A NaCl-templated Fe-TPTZ metal–organic material was formed using facile liquid-assisted grinding/compression. With NaCl, the Fe-TPTZ template-induced stability allows for a rapid, thus, energy-efficient pyrolysis. Among the produced materials, 3D-FeNC-LAG exhibits remarkable performance in ORR (E 1/2 = 0.85 V and E onset = 1.00 V), OER (E j=10 = 1.73 V), and in the zinc–air battery test (power density of 139 mW cm–2). The multilayer stream mapping (MSM) framework is presented as a tool for creating a sustainability assessment protocol for the catalyst production process. MSM employs time, cost, resource, and energy efficiency as technoeconomic sustainability metrics to assess the potential upstream impact. MSM analysis shows that the 3D-FeNC-LAG synthesis exhibits 90% overall process efficiency and 97.67% cost efficiency. The proposed synthetic protocol requires 2 times less processing time and 3 times less energy without compromising the catalyst efficiency, superior to the most advanced methods.

Mechanosynthesis of a bifunctional FeNi–N–C oxygen electrocatalyst via facile mixed-phase templating and preheating-pyrolysis

“…The lower bifunctional activity observed in IroNi-2 and IroNi-1 can be attributed to their lower porosity, which hinders the wetting of the total surface and leads to the inaccessibility and inactivity of a significant portion of active sites. 29 Comparatively, the efficiency of IroNi-3D is found to be on par with that of previously reported FeNi–N–C catalysts (Table S4†), while maintaining the sustainability and cost/energy-efficiency benefits of solid-state synthesis. 28,29…”

“…29 Comparatively, the efficiency of IroNi-3D is found to be on par with that of previously reported FeNi–N–C catalysts (Table S4†), while maintaining the sustainability and cost/energy-efficiency benefits of solid-state synthesis. 28,29…”

“…However, as was demonstrated in our previous studies, a lack of porosity will lead to a lowered electrochemical activity due to poor exposure to catalytically active sites. 29 The C 1s spectrum (Fig. S5a†) displays characteristic peaks at 284.5 and 284.8 eV that can be ascribed to the sp 2 and sp 3 carbons, respectively.…”

“…Currently, most synthetic methods for M–N–C involve solvent-based approaches (dissolution, hydrothermal/solvothermal, and precipitation), which can often generate a substantial quantity of waste and be material, cost, and energy intensive. 28,29 Therefore, in recent studies, mechanosynthesis has been employed as an effective and greener alternative for conventional solvent-based synthesis to reduce or eliminate the generation of waste and material and energy overuse. 30–33 The mechanochemical synthesis is performed in a solid phase where mechanical energy is transferred to reactants by grinding with minimal or no solvent.…”

“…Template-assisted synthesis involves using a scaffold that provides a spatial framework for the desired product once the template is removed to direct the morphology and pore distribution, thereby creating a hierarchical porous structure – a vital characteristic for high-performance catalysts. 29,37 Inorganic compounds (NaCl, KCl, MgO, SiO 2 , Al 2 O 3 , etc. ) are often used in template-assisted synthesis as inexpensive, stable, environmentally friendly, and easy-to-remove compounds.…”