Coupling Bimetallic Oxides/Alloys and N-Doped Carbon Nanotubes as Tri-Functional Catalysts for Overall Water Splitting and Zinc–Air Batteries

Abstract

An effectively multifunctional electrocatalyst is crucial for catalyzing the reactions occurred at electrodes in zinc−air batteries and water splitting cells, such as oxygen evolution reaction (OER), hydrogen evolution reaction (HER), and oxygen reduction reaction (ORR). Herein, two non-noble metal-based multifunctional electrocatalysts of Ndoped carbon nanotubes NCNT/CoFe−CoFe 2 O 4 and NCNT/MnO−(MnFe) 2 O 3 are prepared by a simple solvothermal procedure, followed by two-step annealing under the argon and ammonia atmosphere. The resultant electrocatalysts exhibit good trifunctional performances for HER, ORR, and OER. Notably, the NCNT/CoFe−CoFe 2 O 4 and NCNT/MnO−(MnFe) 2 O 3 assembled zinc−air batteries exhibit high energy densities of 727 and 776 W h kg Zn −1 at the current density of 20 mA cm −2 , respectively. Furthermore, the NCNT/CoFe−CoFe 2 O 4 -based rechargeable zinc−air battery remains excellent durability after discharge−charge cycle testing for 22 h, comparable to the noble metal-based catalyst (Pt/C + IrO 2 )-assembled zinc−air battery. Furthermore, the NCNT/ CoFe−CoFe 2 O 4 and NCNT/MnO−(MnFe) 2 O 3 -assembled water splitting cells need ∼1.65 and 1.70 V, respectively, to deliver a current density of 10 mA cm −2 , lower than that of IrO 2 −Pt/C (1.71 V) and present excellent durability under long-term electrolysis. This work provides a facile strategy to prepare highly active multiple functional electrocatalysts for energy conversion and storage.

Recent advances in transition metal-based electrocatalysts for alkaline hydrogen evolution

“…Hitherto, CoO x , 119-121 VO 2 , 47 MnO 2 , 21,122 and NiO, 118,123 are representatives that possess high catalytic performance after modifications. Hybridizing TMOs with other electroactive materials (e.g., TMOs, [124][125][126] TMPs, 48,127 TMs, 123,128,129 TM alloys, 130,131 TMSs 132,133 ) is an advisable approach to improve the catalytic performance of bare have a more flexible redox property, and higher conductivity than the corresponding individual metal oxides, herein manifesting a better catalytic activity in electrochemistry. 48 However, the electrocatalytic ability of such pristine TMOs in HER is still unsatisfactory.…”

Hollow Porous MnFe2O4 Sphere Grown on Elm‐Money‐Derived Biochar towards Energy‐Saving Full Water Electrolysis

“…[32] For instance, the resulting overpotential of NiFe 2 O 4 /VACNT reaches 150 and 240 mV for the HER and the OER at 10 mA cm À2 . [33] The overall water splittingp rocess can be realized at 10 mA cm À2 under the 1.72 V. The NCNT/CoFe-CoFe 2 O 4 needs 310 and 204 mV overpotential to obtain 10 mA cm À2 for the OER and the HER, respectively, [34] which just performs1 .65 Vt o produce 10 mA cm À2 for the overall water decomposition.I n alkaline solution, the NiCo 2 O 4 with complex necklace-like structure prepared by using an ew adsorption-calcination-reduction method requires overpotentials of 135 and 240 mV for HER and OER to reach1 0mAcm À2 . [35] And a1 .61 Vi sa pplied to obtain 10 mA cm À2 in two-electrode system overall water splitting process.…”

Smart Assembly of Sulfide Heterojunction Photocatalysts with Well‐Defined Interfaces for Direct Z‐Scheme Water Splitting under Visible Light

“…Upon the completion of the cation exchange (CM‐3), a peak at a BE that corresponds to almost pure MnS was observed (Figure c). The peaks of Mn 2p 3/2 and Mn 2p 1/2 are located at BE=642.9 and 653.2 eV, respectively . The BE of Mn 2p in CM‐2 shifts negatively (BE=642.5 and 652.8 eV), which suggests an intimate interaction between the two semiconductors .…”