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Transition metal selenides have attracted intensive interest as cost-effective electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) because of the continuous thrust in sustainable energy conversion. In this article a Mn-based bifunctional electrocatalyst, MnSe, has been identified which shows efficient OER and ORR activity in alkaline medium. The catalytic activity could be further enhanced by using multiwalled carbon nanotubes (MWCNTs) which increases the charge transfer and electronic conductivity of the catalyst composite. This MnSe@MWCNT catalyst composite exhibits a very low overpotential of 290 mV at 10 mA cm −2 , which outperforms state-of-the-art RuO 2 as well as other oxide based electrocatalysts. Furthermore, the composite's facile OER kinetics was evidenced by its small Tafel slope of 54.76 mV dec −1 and low charge transfer resistance, indicating quick transport of the reactant species at the electrode interface. The MnSe@MWCNT also exhibited efficient electrocatalytic activity for ORR with an E onset of 0.94 V, which is among the best reported to date for chalcogenide based ORR electrocatalysts. More importantly, this MnSe-based ORR electrocatalyst exhibits high degree of methanol tolerance, showing no degradation of catalyst performance in the presence of copious quantities of methanol, thereby out-performing the state-of-the-art Pt electrocatalyst. The catalyst composite also exhibited exceptional functional and compositional stability for OER and ORR after a prolonged period of continuous operation in alkaline medium. The surface Raman analysis after OER revealed the retention of manganese selenide surface with evidence of oxo coordination, confirming the formation of an (oxy)selenide as the active surface for OER. Such efficient bifunctional OER and ORR activity makes this MnSe based catalyst attractive for overall electrolysis in regenerative as well as direct methanol fuel cells.
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Kinetically Stable Oxide Overlayers on Mo 3 P Nanoparticles Enabling Lithium–Air Batteries with Low Overpotentials and Long Cycle Life
Abstract The main drawbacks of today's state‐of‐the‐art lithium–air (Li–air) batteries are their low energy efficiency and limited cycle life due to the lack of earth‐abundant cathode catalysts that can drive both oxygen reduction and evolution reactions (ORR and OER) at high rates at thermodynamic potentials. Here, inexpensive trimolybdenum phosphide (Mo3P) nanoparticles with an exceptional activity—ORR and OER current densities of 7.21 and 6.85 mA cm−2at 2.0 and 4.2 V versus Li/Li+, respectively—in an oxygen‐saturated non‐aqueous electrolyte are reported. The Tafel plots indicate remarkably low charge transfer resistance—Tafel slopes of 35 and 38 mV dec−1for ORR and OER, respectively—resulting in the lowest ORR overpotential of 4.0 mV and OER overpotential of 5.1 mV reported to date. Using this catalyst, a Li–air battery cell with low discharge and charge overpotentials of 80 and 270 mV, respectively, and high energy efficiency of 90.2% in the first cycle is demonstrated. A long cycle life of 1200 is also achieved for this cell. Density functional theory calculations of ORR and OER on Mo3P (110) reveal that an oxide overlayer formed on the surface gives rise to the observed high ORR and OER electrocatalytic activity and small discharge/charge overpotentials.
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- PAR ID:
- 10455030
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Materials
- Volume:
- 32
- Issue:
- 50
- ISSN:
- 0935-9648
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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