Fig. 4.

Digital photographs of carbon cloth (a), carbon brush (b), carbon rod (c), carbon mesh (d), carbon veil (e), carbon paper (f), carbon felt (g), granular activated carbon (h), granular graphite (i), carbonized cardboard (j), graphite plate (k), reticulated vitreous carbon (l), stainless steel plate (m), stainless steel mesh (n), stainless steel scrubber (o), silver sheet (p), nickel sheet (q), copper sheet (r), gold sheet (s), titanium plate (t). Effect of the chemistry and morphology on the surface characteristics and bioelectrocatalysis (u) (Fig. 4j adapted from Ref. [228], published by Frontiers, CC BY 3.0 (https://creativecommons.org/licenses/by/3.0/); Fig. 4p, q, r, s adapted from Ref. [229], published by The Royal Society of Chemistry, CC BY 3.0 (https://creativecommons.org/licenses/by/3.0/); Fig. 4t adapted from Ref. [230] with permission of Elsevier; Fig. 4u adapted from Ref. [75] with permission of Elsevier).