Co3O4/CoFe2O4 decorated on nickel foam (NF/Co3O4/CoFe2O4) was synthesized from a metal–organic framework by a solvothermal approach using nicotinic acid as an organic linker followed by annealing at 500 °C. The electrochemical activity of NF/Co3O4/CoFe2O4 for the oxygen evolution reaction (OER) was assessed in alkaline medium. Under basic conditions (pH > 10), the composite electrode revealed enhanced electrocatalytic OER activity requiring an overpotential of 215 mV versus RHE to reach 10 mA cm–2 with a Tafel slope of 90 mV dec–1. The enhanced OER activity was ascribed to the presence of Co3+ and Fe3+ in the octahedral sites of Co3O4 and CoFe2O4, respectively, and their synergic effect in Co3O4/CoFe2O4. This anode showed a stable current density of about 160 mA cm–2 for 20 h; the same Co3O4/CoFe2O4/NF anode was applied for several OER experiments without loss of activity.

Biocatalysts provide a number of advantages such as high selectivity, the ability to operate under mild reaction conditions and availability from renewable resources that are of interest in the development of bioreactors for applications in the pharmaceutical and other sectors. The use of oxidoreductases in biocatalytic reactors is primarily focused on the use of NAD(P)-dependent enzymes, with the recycling of the cofactor occurring via an additional enzymatic system. The use of electrochemically based systems has been limited. This review focuses on the development of electrochemically based biocatalytic reactors. The mechanisms of mediated and direct electron transfer together with methods of immobilising enzymes are briefly reviewed. The use of electrochemically based batch and flow reactors is reviewed in detail with a focus on recent developments in the use of high surface area electrodes, enzyme engineering and enzyme cascades. A future perspective on electrochemically based bioreactors is presented.

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