Electrochemical energy conversion devices and cells, and negative electrode-side materials for them

An electrochemical energy conversion device comprising a stack of solid oxide electrochemical cells alternating with gas separators, wherein each electrochemical cell comprises a layer of solid oxide electrolyte, a negative electrode-side structure on one side of the electrolyte layer and comprising one or more porous layers including a functional layer of negative electrode material having an interface with the one side of the electrolyte layer, and a positive electrode-side structure on the opposite side of the electrolyte layer and comprising one or more porous layers including a layer of positive electrode material having an interface with the opposite side of the electrolyte layer, wherein said electrochemical cell and a first of the gas separators on the negative electrode side of the electrochemical cell at least partly form therebetween a negative electrode-side chamber and said electrochemical cell and a second of the gas separators on the positive electrode side of the electrochemical cell at least partly form therebetween a positive electrode-side chamber, and wherein chemically unbound material selected from one or both of free alkali metal oxygen-containing compounds and free alkaline earth metal oxygen-containing compounds is provided in or on one or more of the negative electrode-side structure, the first gas separator and any other structure of the electrochemical energy conversion device forming the negative electrode-side chamber, the chemically unbound material acting to reduce degradation of electrochemical performance on the negative electrode side of the electrochemical energy conversion device during use of the device, and wherein if the chemically unbound material is provided in the functional layer of negative electrode material there is no chemically unbound material present at the interface of that layer with the electrolyte layer.