Electrode, membrane electrode assembly, electrochemical cell, and stack

An electrode comprising:

• a base material;
• and
• a catalyst layer provided on the base material, the catalyst layer including a plurality of catalyst units having a porous structure, wherein
• the catalyst layer comprises a first catalyst layer and a second catalyst layer, wherein the first catalyst layer is located between the base material and the second catalyst layer, the first catalyst layer including a plurality of first catalyst units dispersed at a first dispersion degree, the plurality of the first catalyst units being a plurality of carrierless catalyst units having a porous structure or a laminated structure including a void layer, the second catalyst layer including a plurality of second catalyst units dispersed at a second dispersion degree, the plurality of the second catalyst units being a plurality of carrierless catalyst units having a porous structure or a laminated structure including a void layer,
• the first catalyst layer and the second catalyst layer are laminated,
• the second catalyst layer has a catalyst structure in which columnar structures extending in the laminated direction of the first catalyst layer and the second catalyst layer are bundled,
• the bundled columnar structures are arranged in a direction parallel to the first catalyst layer,
• the second dispersion degree is 10 nm or more different from the first dispersion degree,
• the first catalyst units have the laminated structure including a plurality of nanosheet-like catalysts and void layers each existing between the two corresponding nanosheet-like catalysts,
• the laminated structure is directly connected with the bundled columnar structures, and
• an average height of the second catalyst units is not less than 50 nm and not more than 800 nm.