Electroactive enzymes are of interest for their ability to catalyze the formation of high-energy chemicals, such as molecular hydrogen or methane, using electricity as a feedstock. However, much work remains in enzyme characterization and system optimization to achieve industrially relevant enzymatic electrocatalysts for energy storage. In the presented work, a key enzyme from the methanogenic archaeon Methanococcus maripaludis, heterodisulfide reductase super complex (HdrSC), is characterized for its ability to form either molecular hydrogen or formate at an electrode. The ability of the redox polymer cobaltocene-functionalized polyallylamine (Cc-PAA) to mediate electron transfer to HdrSC, along with other hydrogenases, is then discussed. Cc-PAA allows for high enzyme concentration to be achieved at the electrode, and greatly enhances electrosynthetic enzyme activity, with mediated rates approaching the maximum observed turnover rates. Further optimization of such robust and versatile enzymes and mediators such as HdrSC and Cc-PAA is necessary to achieve renewable, efficient energy storage solutions.