Oxygen electrode catalytic layer for reversible, alkaline or anion exchange membrane electrochemical devices
Oxygen electrodes, production methods and reversible, alkaline or anion exchange membrane (AEM) electrochemical devices are provided. The oxygen electrodes are operable in the reversible devices both as cathodes of a fuel cell supporting an oxygen reduction reaction (ORR), and as anodes of an electrolyzer supporting an oxygen evolution reaction (OER). The oxygen electrodes comprise a substrate layer which may be a porous transport layer (PTL), possibly coated and/or hydrophobized, or a membrane; and a blend of catalysts which is deposited on the substrate layer to form a catalyst layer, and includes ORR catalyst (e.g., a platinum group metal), OER catalyst (e.g., nickel-based particles), and possibly binders such as ionomers, PTFE or other polymers that are resistant in alkaline environment, but with the catalyst layer and the substrate layer being devoid of elemental carbon.
1 . A dual, reversible, alkaline or anion exchange membrane (AEM) electrochemical device that is operable both as a fuel cell and as an electrolyzer, the device comprising:
an oxygen electrode comprising:
a substrate layer that is devoid of elemental carbon, and
a catalyst layer deposited on the substrate layer, the catalyst layer comprising a blend of an oxygen reduction reaction (ORR) catalyst comprising at least one platinum group metal (PGM) and an oxygen evolution reaction (OER) catalyst comprising nickel iron layered double hydroxide (NiFeLDH) particles, wherein the catalyst layer is devoid of elemental carbon;
wherein the oxygen electrode is operable in a strongly alkaline environment as an anode to evolve oxygen in the OER when the alkaline or AEM device is operated as an electrolyzer, and as a cathode to reduce oxygen gas in the ORR when the alkaline or AEM device is operated as a fuel cell, over repeated cycles of operation,
an electrode supporting a hydrogen oxidation reaction (HOR) when the alkaline or AEM device is operated as the fuel cell, and supporting a hydrogen evolution reaction (HER) when the alkaline or AEM device is operated as the electrolyzer, and
a strongly alkaline electrolyte contacting the electrodes.
2 . The device of claim 1 , wherein the substrate layer comprises a porous transport layer (PTL).
3 . The device of claim 1 , wherein the substrate layer comprises a membrane, onto which the catalyst layer is deposited, and the oxygen electrode is part of a catalyst coated membrane (CCM).
4 . The device of claim 3 , wherein the CCM is coated on one side by the blend of ORR catalyst and OER catalyst, and on another side by a catalyst blend supporting a hydrogen oxidation reaction (HOR) when the device is operated as the fuel cell, and hydrogen evolution reaction (HER) when the device is operated as the electrolyzer.
5 . The dual device of claim 4 , configured to operate with dry oxygen during fuel cell operation of the device.
6 . The device of claim 1 , wherein the blend further comprises at least one binder comprising at least one ionomer.
7 . The device of claim 1 , further configured to operate with dry oxygen during fuel cell operation of the device.
8 . A method of preparing a reversible, alkaline or anion exchange membrane (AEM) electrochemical device that is operable both as a fuel cell with the oxygen electrode supporting an oxygen reduction reaction (ORR) as a cathode of the fuel cell, and as an electrolyzer with the oxygen electrode supporting an oxygen evolution reaction (OER) as an anode of the electrolyzer, the method comprising:
preparing an oxygen electrode by:
blending an ORR catalyst comprising at least one platinum group metal (PGM) and an OER catalyst comprising nickel iron layered double hydroxide (NiFeLDH) particles, the blend being devoid of elemental carbon, and
depositing the blend on a substrate layer that is devoid of elemental carbon to form the oxygen electrode,
wherein said oxygen electrode is operable in an alkaline environment having a pH of 12 or more to evolve oxygen in an OER reduce oxygen gas in an ORR after repeated cycles of operation as a fuel cell and an electrolyzer; and
constructing the device with the oxygen electrode and an electrode supporting a hydrogen oxidation reaction (HOR) when the device is operated as the fuel cell, and supporting the hydrogen evolution reaction (HER) when the device is operated as the electrolyzer, and a strongly alkaline electrolyte contacting the electrodes.
9 . The method of claim 8 , wherein the substrate layer comprises a porous transport layer (PTL).
10 . The method of claim 8 , wherein the substrate layer comprises a membrane, and the oxygen electrode is part of a catalyst coated membrane (CCM).
11 . The method of claim 10 , further comprising coating the CCM on one side by the blend of ORR catalyst and OER catalyst, and on another side by a catalyst blend supporting a hydrogen oxidation reaction (HOR) when the device is operated as the fuel cell, and hydrogen evolution reaction (HER) when the device is operated as the electrolyzer.
12 . The method of claim 8 , wherein the blend further comprises at least one binder comprising one or more: ionomer, PTFE, and polymer resistant in alkaline environment.
13 . The method of claim 8 , further comprising configuring the oxygen electrode to operate with dry oxygen during fuel cell operation of the device.
14 . The method of claim 8 , further comprising selecting the OER catalyst to not degrade during fuel cell operation of the device, and the ORR catalyst to not degrade during electrolyzer operation of the device.
15 . The device of claim 1 , wherein said oxygen electrode evolves oxygen in the OER at a voltage below 2.0 V at a current density above 0.2 A/cm 2 and reduces oxygen gas in the ORR at a voltage greater than 0.4 V at a current density above 0.2 A/cm 2 after repeated cycles of operation as a fuel cell and an electrolyzer.
16 . An alkaline or anion exchange membrane (AEM) electrolyzer comprising:
an oxygen electrode comprising:
a substrate layer that is devoid of elemental carbon, and
a catalyst layer deposited on the substrate layer, the catalyst layer comprising a an oxygen evolution reaction (OER) catalyst comprising nickel iron layered double hydroxide (NiFeLDH) particles, wherein the catalyst layer is devoid of elemental carbon;
wherein the oxygen electrode is operable in an alkaline environment having a pH of 12 or more as an anode to evolve oxygen in the OER over repeated cycles of operation, and
an electrode supporting a hydrogen evolution reaction (HER),
wherein the electrodes contact a strongly alkaline electrolyte.
17 . The device of claim 1 , wherein the blend further comprises at least one binder and the oxygen electrode is hot-pressed for a period of up to ten minutes at around the glass temperature of the binder to enhance its stability, homogeneity and increase its operational durability.
18 . The electrolyzer of claim 16 , wherein the substrate layer comprises a porous transport layer (PTL).
19 . The electrolyzer of claim 16 , wherein the substrate layer comprises a membrane, onto which the catalyst layer is deposited, and the oxygen electrode is part of a catalyst coated membrane (CCM).
20 . The electrolyzer of claim 16 , wherein the catalyst layer further comprises at least one binder comprising at least one ionomer.
21 . The electrolyzer of claim 16 , wherein the catalyst layer further comprises at least one binder and the oxygen electrode is hot-pressed for a period of up to ten minutes at around the glass temperature of the binder to enhance its stability, homogeneity and increase its operational durability.