For 10 points, name this element formed at the cathode when water is electrolyzed, which is formed by reducing protons.
A January 2016 Nature paper described a P22 phage capsid that reduces this element.  This element gets oxidized by liquid bromine in a proposed membrane-less battery that operates using laminar flow. Titanium dioxide reduces this element under sunlight in the Honda-Fujishima effect. Enzymes that oxidize this element have double metal clusters of nickel or iron in their active sites. The reduction of this element is the net reaction of the cerium (IV)-cerium (III) or (*) sulfur-iodine cycles. This element is the final electron acceptor of the four electrons liberated in the S-state cycle. This element gets oxidized in the water-gas shift reaction and the Fischer-Tropsch reaction. This element gets oxidized in a fuel cell. Its standard reduction potential is defined to be 0. For 10 points, name this element formed at the cathode when water is electrolyzed, which is formed by reducing protons.
A January 2016 Nature paper described a P22 phage capsid that reduces this element.  
hydrogen gas [or H2]