Investigation of Transition Metal-Based (Mn, Co, Ni, Fe) Trimetallic Oxide Nanoparticles on N-doped Carbon Nanotubes as Bifunctional Catalysts for Zn-Air Batteries

Abstract

Various transition metal-based bimetallic and trimetallic oxides on N-CNTs were successfully synthesized in a one-pot process. Porous gas diffusion layers (GDLs) were simultaneously impregnated with the catalysts during synthesis, resulting in an efficient and scalable preparation technique for nano-composite air electrodes. NiMnO x /N-CNT, NiFeO x /N-CNT, and (Co,Fe) 3 O 4 /N-CNT catalysts were the highest performing bimetallic oxides based on battery rate test results. Therefore, Ni-Co-Fe, Ni-Mn-Fe, and Mn-Co-Fe systems were investigated as combined trimetallic oxide/N-CNT catalysts for Zn-air batteries. Trimetallic oxides on N-CNTs exhibited improved OER activity and comparable ORR activity relative to the bimetallic oxide catalysts in linear sweep voltammetry (LSV) tests. Discharge/charge efficiencies for tri-metallic oxides on N-CNTs calculated from battery rate test measurements at a current density of 20 mA cm −2 were 60.5%, 60.7%, and 60.0% for NCFO/N-CNT, NMFO/N-CNTs and MCFO/N-CNT, respectively. Bifunctional cycling of all trimetallic oxide/N-CNT electrodes at 10 mA cm −2 for 100 h showed excellent stability, particularly the NCFO/N-CNT catalyst. Additionally, the efficiencies for NCFO/N-CNT, NMFO/N-CNT and MCFO/N-CNT samples were 58.5%, 57.9% and 57.2%, respectively, after cycling, which compare favorably with that of Pt-Ru/C (55.3%). Trimetallic oxides on N-CNTs are, therefore, excellent candidates as high performing, non-precious metal catalysts for Zn-air batteries.

Zn‐Based Oxides Anchored to Nitrogen‐Doped Carbon Nanotubes as Efficient Bifunctional Catalysts for Zn‐Air Batteries

“…Both catalysts show precipitation of the oxide particles near N defects in the nanotube wall, which is likely due to the reduced free energy for nucleation at defect sites. This phenomenon was also observed in our previous studies …”

“…Recently, we have reported good bifunctional activity of transition metal oxide spinel nanoparticles anchored to N‐CNTs via a simple precipitation and impregnation technique . The combination of metal oxides and doped carbon materials has been previously reported to show improvements towards the oxygen reactions .…”

“…The catalysts are simultaneously synthesized and deposited onto the air electrode via an impregnation technique which has been shown to improve battery performance . Further discussion of the impregnation technique can be found in our previous studies . The resulting catalysts are compared electrochemically with their respective non‐Zn oxides to better understand the effects of Zn incorporation.…”

Heterogeneous Trimetallic Nanoparticles as Catalysts

“…Perhaps one of the most compelling properties of multimetallic NPs is the many structures they can manifest. TMNPs with varied morphologies, such as wires, − dumbbells, hollow interiors, ,− nanotubes, , and dendrimers, − have been reported, exemplifying the flexible outcomes available through variation of the synthesis conditions and metal choice. Interestingly, the different metals within NPs can be distributed in many ways on and within the nanoparticle.…”

Synergistic Effect of Co9S8 and FeS2 Inlaid on N-Doped Carbon Nanofibers toward a Bifunctional Catalyst for Zn–Air Batteries

“…Recently, transition-metal-based materials, such as transition-metal oxides, sulfides, , and others, − have been considered to be a promising class of alternatives. However, the less synergistic effects of intrinsic catalytic activity, selectivity, and conductivity of these materials still hinder their widespread application .…”