Catalyst layer, method for producing the same, membrane electrode assembly and electrochemical cell
Embodiments of the present disclosure aim to provide a catalyst layer ensuring a high cell voltage and having both excellent robustness and sufficient endurance, and also to provide a process for producing the layer, a membrane electrode assembly and an electrochemical cell. The catalyst layer comprises two or more noble metal-containing layers, and a porous ceramic layer placed between the noble metal-containing layers. Further, in the catalyst layer, voids exist between the porous ceramic layer and the noble metal-containing layers.
1. A catalyst layer, comprising:
two or more noble metal-containing layers which consist of a metal or metal alloy; and
a porous ceramic layer placed between said noble metal-containing layers,
wherein
void layers exist between said porous ceramic layer and said noble metal-containing layers, wherein said noble metal-containing layer and said porous ceramic layer have a fused portion of said noble metal-containing layer and said porous ceramic layer at an edge thereof, the fused portion connecting said noble metal-containing layer and said porous ceramic layer physically such that main surfaces of said noble metal-containing layer and said porous ceramic layer are kept separate via the void layer, and
said porous ceramic layer has a composition different from a composition of said noble metal-containing layer, and consists of:
an oxide or mixed oxide of at least one element of Ta, Sn, Zr, W and Nb;
optionally at least one metal selected from the group consisting of Mn, Fe, Co, Ni, Zn, Sn, Al, and Cu;
optionally an oxide of at least one metal selected from the group consisting of Mn, Fe, Co, Ni, Zn, Al, and Cu; and
optionally a nitride of at least one metal selected from the group consisting of Mn, Fe, Co, Ni, Zn, Sn, Al, and Cu.
2. The catalyst layer according to claim 1 , further comprising fibrous carbons placed between said porous ceramic layer and said noble metal-containing layers.
3. The catalyst layer according to claim 1 , wherein the maximum distance from said porous ceramic layer to said noble metal-containing layers is 10 nm to 300 nm inclusive.
4. The catalyst layer according to claim 1 , wherein said noble metal-containing layers contain voids therein and the void contents thereof are 20 to 80 vol % inclusive.
5. The catalyst layer according to claim 1 , wherein said porous ceramic layer contains voids therein and the void content thereof is 20 to 80 vol % inclusive.
6. The catalyst layer according to claim 1 , wherein said porous ceramic layer has a thickness of 5 to 100 nm inclusive.
7. The catalyst layer according to claim 1 , wherein said noble metal-containing layers contain Pt.
8. The catalyst layer according to claim 1 , wherein said noble metal-containing layers contain an alloy represented by Pt y Ru z T 1-y-z , wherein 0.2≤y≤0.8, 0≤z≤0.8, and T represents at least one element selected from the group consisting of W, Hf, Si, Mo, Ta, Ti, Zr, Ni, Co, Nb, V, Sn, Al and Cr.
9. The catalyst layer according to claim 1 , wherein said noble metal-containing layers contain an alloy represented by Pt u M 1-u , wherein 0<u≤0.9 and M represents at least one element selected from the group consisting of Co, Ni, Fe, Mn, Ta, W, Hf, Si, Mo, Ti, Zr, Nb, V, Cr, Al and Sn.
10. The catalyst layer according to claim 1 , wherein the maximum distance between adjacent two of said noble metal-containing layers is 10 to 400 nm inclusive.
11. The catalyst layer according to claim 1 , wherein the oxide or mixed oxide of at least one element of Ta, Sn, Zr, W and Nb included in said porous ceramic layer is selected from the group consisting of NiTaO, WNbO and ZrTaO.
12. The catalyst layer according to claim 1 , wherein said porous ceramic layer contains voids therein and the void content thereof is 30 to 80 vol % inclusive.