Stable Acidic Water Oxidation with a Cobalt–Iron–Lead Oxide Catalyst Operating via a Cobalt‐Selective Self‐Healing Mechanism

Abstract

The instability and expense of anodes for water electrolyzers with acidic electrolytes can be overcome through the implementation of a cobalt‐iron‐lead oxide electrocatalyst, [Co–Fe–Pb]Ox, that is self‐healing in the presence of dissolved metal precursors. However, the latter requirement is pernicious for the membrane and especially the cathode half‐reaction since Pb2+ and Fe3+ precursors poison the state‐of‐the‐art platinum H2 evolving catalyst. To address this, we demonstrate the invariably stable operation of [Co–Fe–Pb]Ox in acidic solutions through a cobalt‐selective self‐healing mechanism without the addition of Pb2+ and Fe3+ and investigate the kinetics of the process. Soft X‐ray absorption spectroscopy reveals that low concentrations of Co2+ in the solution stabilize the catalytically active Co(Fe) sites. The highly promising performance of this system is showcased by steady water electrooxidation at 80±1 °C and 10 mA cm−2, using a flat electrode, at an overpotential of 0.56±0.01 V on a one‐week timescale.

Durable Electrooxidation of Acidic Water Catalysed by a Cobalt‐Bismuth‐based Oxide Composite: An Unexpected Role of the F‐doped SnO2 Substrate

“…The semi‐logarithmic polarisation plot constructed using the quasi‐stabilised potentials at the examined current densities was close to linear within the investigated narrow range with a corresponding E vs . log j (Tafel) slope of ca 0.08 V dec −1 (Figure 7b), which is close to the results previously reported for other OER catalysts operating in electrolyte solutions with low pH [17,36] . Tests at very high current densities up to 400 mA cm −2 revealed a notable increase in the E vs .…”

“…RHE (Figure S18). Such behaviour strongly resembled that reported for self‐healing water oxidation electrocatalysts operating at different pH in the presence of mM‐level concentrations of the metal precursors [16–17,26b,37] . In contrast, the Co−Bi−Sn‐based system reported herein could be electrooxidatively reformed from negligibly small quantities of the precursors leached into the solution from the very thin catalytic film.…”

“…RHE) is inferior yet comparable to that of the [Co−Fe−Pb]O x catalyst tested at the same pH in the presence of the cobalt precursor only (100 mA cm −2 at ca 1.96 V vs . RHE) [17] . However, our major aim herein was to develop and investigate a catalytic system that can operate in the absence of the intentionally added precursors to the electrolysed solution.…”

“…The lead(IV) oxide matrix has also recently been used as a backbone of a self‐healing [Co−Fe−Pb]O x catalytic system that can operate at very high current densities, low pH and temperatures up to 80 °C with uncompromised stability, but in the presence of relatively high (mM) concentrations of dissolved metal precursors [16] . The latest advancement of the [Co−Fe−Pb]O x system was the demonstration of its operation in the presence of low amounts (μM) of Co 2+ only through a cobalt‐selective self‐healing mechanism [17] . Other elements employed in attempts to create an acid‐stable matrix for the water electrooxidation catalysts include antimony, [18] chromium, [19] tantalum, [20] tin, [20b,21] titanium, [22] and yttrium [23] .…”

“…One element that has not yet been actively investigated in this context is bismuth – a metal that is sometimes considered as chemically most suitable for the substitution of lead, [25] a key component of some of the most acid stable WOR catalysts [3b,16–17,26] . Pourbaix diagrams (Figure S1) for lead and bismuth in the low pH range are qualitatively similar, [27] which further motivated us to investigate the capability of Bi oxides (BiO x ) to act as a stabilising component for WOR catalysts operating in acidic solutions and obtained by a simple electrodeposition technique.…”