Abstract: An electrochemical cell comprises at least the following layers stacked in the following order: a first electrode layer, an electrolyte layer, a second electrode layer, a current collector layer, and a protective cover; the protective cover comprising an electrically-insulating material. The cell further comprises an electrically-conductive contact pad that is configured to enable connection of the cell to external devices, the contact pad being provided on an external side of the protective cover that is opposed to the current collector layer, and comprising an exposed surface that is bounded about its perimeter by the electrically-insulting material. An electrically-conductive pathway is provided between the contact pad and the current collector layer, the electrically-conducive pathway extending through the protective cover and contacting a face of the current collector layer at a connection site.

Abstract: A composition consisting essentially of a perovskite crystalline structure includes ions of a first metal M1 which occupies an A-site of the perovskite crystalline structure and ions of a second metal M2 which occupies a B-site of the perovskite crystalline structure. M2 has two oxidation states capable of forming a redox couple suitable for reversibly catalyzing an oxygen reduction reaction (ORR) and an oxygen evolution reaction (OER). The composition also includes ions of a third metal M3 at least a portion of which substitutes for M1 in the A-site of the perovskite crystalline structure, and at least a portion of which optionally also substitutes for M2 in the B-site of the perovskite crystalline structure. At least some of the ions of M3 have a different oxidation state to the ions of M1. The composition also includes atoms of an element X, which is a chalcogen.

Abstract: A composition consisting essentially of a perovskite crystalline structure, the composition comprising: ions of a first metal M1 which occupies an A-site of the perovskite crystalline structure; ions of a second metal M2 which occupies a B-site of the perovskite crystalline structure, M2 having two oxidation states capable of forming a redox couple suitable for reversibly catalyzing an oxygen reduction reaction (ORR) and an oxygen evolution reaction (OER); ions of a third metal M3 at least a portion of which substitutes for M1 in the A-site of the perovskite crystalline structure, and at least a portion of which optionally also substitutes for M2 in the B-site of the perovskite crystalline structure, at least some of the atoms M3 having a different oxidation state to the atoms M1; and atoms of an element X, which is a chalcogen; wherein the metal ions M1, M2 and M3 are present in the atomic ratios (a) or (b): (a) 25 to 49.