The establishment of an economic means of hydrogen production by electrochemical water‐splitting can help alleviate the intermittency problem associated with renewable energy sources such as solar and wind, and also provide for the extensive commercialization of fuel cell technologies. To enable this, cheap, active, and stable hydrogen evolution catalysts that can replace precious metal catalysts such as Pt must be developed. Herein, a scalable synthesis of porous Mo2C nanostructures derived from biochar, an inexpensive plant byproduct, is reported. The Mo2C catalyst materials prepared using this solid‐state method, loaded on planar substrates, require overpotentials of only 35 and 60 mV to drive current densities of −10 and −100 mA cm−2 in 0.50 m H2SO4 solution and exhibit stable operation for >100 h at operating current densities of −10 and −100 mA cm−2.

The photocathodic properties of cuprous oxide enable the light-directed patterning of electodeposited thin films.

The galvanic replacement (GR) reaction of Au on Cu2O is mediated by the disproportionation of the substrate. As a result, the morphology of the deposited film can be controlled by the chemical conditions.