Development of ceramics for use in proton conducting ceramic cells

Siddiq, Abubakr (2024). Development of ceramics for use in proton conducting ceramic cells. University of Birmingham. Ph.D.

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Abstract

Proton conducting ceramics (PCCs) can incorporate water molecules into oxide ion vacancies and then transfer protons (H+) via the oxide ions. Thus, enabling these PCCs to be implemented as part of a fuel cell or an electrolyser, that can operate within the intermediate temperature range of 500°C to 700°C. Within a proton conducting ceramic electrolyser (PCCE) dry H2 is able to be produced, unlike in oxide conducting solid oxide electrolyser (OC-SOE).

The electrolyte materials used in these cases have been firmly established, however there is still an array of materials that can be explored as electrodes for proton conducting ceramic cells (PCCCs). Previously, compositions used for oxide conducting solid oxide cells (OC-SOCs) have been utilised in PCCCs. This thesis aims to develop electrode materials that can be utilised in PCCC within the intermediate temperature range.
The electrode material barium ferrite (BaFeO3-δ) was synthesised and doped with niobium (Nb) and bismuth (Bi); their lattice parameters were confirmed by X-ray diffraction (XRD). Nb-doped samples were chemically stable in humid N2 atmospheres. Conversely, Bi doped samples only remained stable in humid N2, in dry N2 these samples formed two phases.

Ruddlesden-Popper; La2-x(Ba/Sr)xNiO4+δ, La3-xPrxNi2O7-δ and La4-xPrxNi3O10-δ were synthesised for electrode materials; again XRD confirmed their lattice parameters. Under humid N2, La2NiO4+δ, La1.5Sr0.5NiO4+δ, La3Ni2O7-δ, La2PrNi2O7-δ, La4Ni3O10-δ, La3.75Pr0.25Ni3O10-δ and La3PrNi3O10-δ were shown to maintain their XRD pattern.

BaCe0.6Zr0.3Y0.1O3-δ electrolyte pellets were manufactured by pressing and sintering with 1 wt% nickel oxide (NiO) as a sintering aid. Symmetrical cells tests were performed in dry and humid air conditions. La2NiO4+δ and La1.5Sr0.5NiO4+δ were shown to have a decrease in polarisation resistance when measurements were taken in humid air, below 600°C. All other samples showed an increase in polarisation resistance when measurements were taken in humid air, suggesting p-type conductivity.

Following symmetrical cell testing, fuel cell tests were performed on La2NiO4+δ. A power density of 4.94 mWcm-2 was achieved, the cell was then tested in electrolyser mode and a current density of 3.29 mAcm-2 was achieved at 700°C. Electrolysis testing was then performed using La3Ni2O7-δ as the air electrode 21.3 mAcm-2 was achieved at 700°C, suggesting La3Ni2O7-δ to be a better performing electrode then La2NiO4+δ for electrolysis.

Overall, it has been shown that La2NiO4+δ and La3Ni2O7-δ can be utilised in PCCCs. Implying other Ruddlesden-Popper compositions may also be viable for use in a fuel cell or electrolyser, such as La3 xPrxNi2O7-δ and La4-xPrxNi3O10-δ. With La4Ni3O10-δ possibly being a better performing air electrode, for electrolysis, than La3Ni2O7-δ, as it has a greater number of corner linked NiO6 octahedra.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):