The
development of an efficient catalyst for the oxygen evolution
reaction (OER) is critical to fulfilling the mission of hydrogen generation
by water splitting. Various multicomponent systems have been investigated
so far for the OER, although a systematic investigation is lacking
and there are discrepancies as to which formulations make the best
catalyst. Here, we perform a systematic investigation of a ternary
Ni-Fe-Co oxide gradient library for the OER, using a combinatorial
approach. This approach allows a much faster investigation of a vast
compositional space compared to the traditional step by step approach.
Also, it enables a more reliable comparison of the various catalysts
as they all experience the same process and measurement conditions.
We used the spray pyrolysis technique in combinatorial electrocatalyst
screening for the first time for the generation of a gradient library
of Ni-Fe-Co oxides. Combinatorial electrochemical screening using
a scanning droplet cell (SDC) set up allowed the study of 94 different
points in the compositional space of the trimetallic Ni-Fe-Co oxide
library, which was used to deduce a composition–activity relationship.
At 10 mA cm–2, the investigated points spanned an
overpotential window of 294–320 mV, with the best performing
ternary oxides being confined to a compositional space of 4–15%
Fe, 4–15% Co, and 80–90% Ni. This study provides a foundation
for broad exploration of other mixed-metal oxide combinations.
Pt−Ni polyhedral nanoparticles (NPs) are extensively studied as electrocatalysts, mainly for oxygen reduction reaction (ORR), but they display a poor activity for the oxygen evolution reaction (OER). Here, ultralow platinum Pt@Ni@Pt core−bishell nanorods were designed (less than 1 wt % of Pt), synthesized, and characterized to yield bifunctional electrocatalysts with high efficiency toward ORR and OER in alkaline media. Ultralow platinum Pt@Ni@Pt core−bishell nanorods achieve an unprecedented (for a Pt-based catalyst) overpotential of 0.29 V at 10 mA cm −2 and current density of 162 mA μg −1 Pt at 1.6 V (vs RHE) for the OER, while still maintaining a very decent value of 0.32 A mg −1 Pt at 0.85 V for the ORR. These values outperform the standard Pt catalyst for the ORR and the Ni catalyst for the OER, using less than 1 wt % Pt. We describe the twostep synthesis of the Pt@Ni@Pt nanorods, demonstrating the adjustment of their structural properties by a combination of dimethylformamide (DMF) and benzyl alcohol in a solvothermal reaction. We found that the solvent ratio controls the Pt-core size, Ni-shell thickness, and morphology. The combination of high performance and structure control via synthesis makes Pt@Ni@Pt nanorods promising candidates for further applications and opens a door for their further investigation.
The oxygen reduction reaction (ORR) is a key process in anion exchange membrane fuel cells. The alkaline conditions should allow silver‐based cost‐efficient catalysts to replace platinum group metal materials. However, Ag electrochemical stability or lack of stability in alkaline medium is still to be demonstrated. Herein, Ag catalyst nanoparticles (NPs) are characterized by identical location transmission electron microscopy and X‐ray photoelectron spectroscopy after electrochemical cycling, revealing the losses of activity and surface. Herein, a facile method for enhancing the chemical stability of Ag catalysts in an alkaline environment by depositing a protective polydopamine (PDA) coating is reported. It is enhanced via crosslinking with polyethyleneimine (PEI), on the surface of Ag NPs. The enhanced electrochemical stability of Ag PDA–PEI nanocatalyst via the analysis of ORR polarization curves during accelerated stress test cycling is demonstrated, with at least one order of magnitude higher durability than the standard Pt/C catalyst. Moreover, electrochemical measurements indicate that the protective PDA–PEI coating has good permeability to O2, with a positive effect on the ORR activity of Ag NPs.
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