A modular, multicomponent catalyst design principle is introduced and exemplified using a three-component, oxygen reduction reaction/oxygen evolution reaction (ORR/OER) catalyst designed for the oxygen electrode of unitized reversible fuel cells (URFCs). The catalyst system exhibited unprecedented catalytic performance in liquid electrolyte and in single unitized reversible fuel cell tests. The distinct components, each active for either ORR or OER, are prepared and optimized independently of each other and physically mixed during electrode preparation. The new modular URFC catalyst, Cu-α-MnO 2 /XC-72R/NiFe-LDH, combined a carbon-supported, Cu-stabilized α-MnO 2 ORR catalyst with a NiFe-LDH OER catalyst and displayed improved activity and stability under URFC cycling compared to platinum group metal references.Stepwise modular optimization of the carbon and the interlayer anions of the OER component led to a further improved derivative, Cu-α-MnO 2 /O-MWCNTs/NiFe-LDH-Cl − . This URFC catalyst outperformed all previous materials in terms of its combined overpotential η ORR-OER and performance stability in the rotating disk electrode (RDE) scale. Its single-cell performance is analyzed and discussed.
Anion exchange membrane water electrolysis (AEMWE) is
an attractive
emerging green hydrogen technology. However, the scaling of trends
in activity of anode catalysts for the oxygen evolution reaction (OER)
from a liquid-electrolyte, three-electrode environment to the two-electrode
single-cell format has remained poorly considered. Herein, we critically
investigate the scaling of kinetic and catalytic properties of a family
of highly active Ni foam (NF) supported, anion (A–)-tuned NiFe(-A–)-OER catalysts. Trends in catalytic
activity suggest impressive improvements of up to 91-fold in three-electrode
setups (3LC) compared to uncoated NF. While we demonstrate the successful
qualitative structure–performance tunability in a 5 cm2 AEMWE single cell, we also find serious limitations in the
quantitative predictability of three-electrode setups for single-cell
performance trends. Cell environments appear to equalize the cell
performances of designer catalysts, which has important ramifications
for electrode development. We succeed in analyzing and discussing
some of these translation limitations in terms of previously overlooked
effects summarized in the activity improvement factor f.
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