Axially-integrated epitaxially-grown tandem wire arrays

A plurality of vertically aligned nano- or micro-wires, each nano- or micro-wire of the plurality of nano- or micro-wires comprising:

• at least one first segment comprising a first semiconducting material, and
• at least one second segment comprising a second semiconducting material different than the first semiconducting material,
• wherein the at least first segment and the at least second segment are axially integrated
• wherein each first segment of the at least one first segment is separated from each second segment of the at least one second segment by an ohmic contact, wherein the ohmic contact has a graded composition to obtain lattice matching and includes a tunnel junction,
• wherein each nano- or micro-wire of the plurality of nano- or micro-wires has a dimension comprising a mean diameter of about 500 nm to about 10 micrometers and a mean length of about 1 micrometer to 1 mm and having an aspect ratio of greater than 1;
• wherein at least a portion of each nano- or micro-wire of the plurality of nano- or micro-wires contacts a liquid and wherein at least one end of each nano- or microwire of the plurality of nano- or micro-wires is coated with a hydrogen or oxygen evolution catalyst;
• and
• each nano- or micro-wire of the plurality of nano- or micro-wires is partially embedded in an ion conducting material with the at least one end coated with the hydrogen or oxygen evolution catalyst is free of the ion conducting material.