Hydroxide‐exchange membrane fuel cells can potentially utilize platinum‐group‐metal (PGM)‐free electrocatalysts, offering cost and scalability advantages over more developed proton‐exchange membrane fuel cells. However, there is a lack of non‐precious electrocatalysts that are active and stable for the hydrogen oxidation reaction (HOR) relevant to hydroxide‐exchange membrane fuel cells. Here we report the discovery and development of Ni3N as an active and robust HOR catalyst in alkaline medium. A supported version of the catalyst, Ni3N/C, exhibits by far the highest mass activity and break‐down potential for a PGM‐free catalyst. The catalyst also exhibits Pt‐like activity for hydrogen evolution reaction (HER) in alkaline medium. Spectroscopy data reveal a downshift of the Ni d band going from Ni to Ni3N and interfacial charge transfer from Ni3N to the carbon support. These properties weaken the binding energy of hydrogen and oxygen species, resulting in remarkable HOR activity and stability.
The hydroxide‐exchange membrane fuel cell (HEMFC) is a promising energy conversion device. However, the development of HEMFC is hampered by the lack of platinum‐group‐metal‐free (PGM‐free) electrocatalysts for the hydrogen oxidation reaction (HOR). Now, a Ni catalyst is reported that exhibits the highest mass activity in HOR for a PGM‐free catalyst as well as excellent activity in the hydrogen evolution reaction (HER). This catalyst, Ni‐H2‐2 %, was optimized through pyrolysis of a Ni‐containing metal‐organic framework precursor under a mixed N2/H2 atmosphere, which yielded carbon‐supported Ni nanoparticles with different levels of strains. The Ni‐H2‐2 % catalyst has an optimal level of strain, which leads to an optimal hydrogen binding energy and a high number of active sites.
Acidic water electrolysis enables the production of hydrogen
for
use as a chemical and as a fuel. The acidic environment hinders water
electrolysis on non-noble catalysts, a result of the sluggish kinetics
associated with the adsorbate evolution mechanism, reliant as it is
on four concerted proton-electron transfer steps. Enabling a faster
mechanism with non-noble catalysts will help to further advance acidic
water electrolysis. Here, we report evidence that doping Ba cations
into a Co3O4 framework to form Co3–x
Ba
x
O4 promotes
the oxide path mechanism and simultaneously improves activity in acidic
electrolytes. Co3–x
Ba
x
O4 catalysts reported herein exhibit an
overpotential of 278 mV at 10 mA/cm2 in 0.5 M H2SO4 electrolyte and are stable over 110 h of continuous
water oxidation operation. We find that the incorporation of Ba cations
shortens the Co–Co distance and promotes OH adsorption, findings
we link to improved water oxidation in acidic electrolyte.
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