Biochar (BCH) is a carbon-based bio-material produced from thermochemical conversion of biomass. Several activation or functionalization methods are usually used to improve physicochemical and functional properties of BCHs. In the context of green and sustainable future development, activated and functionalized biochars with abundant surface functional groups and large surface area can act as effective catalysts or catalyst supports for chemical transformation of a range of bioproducts in biorefineries. Above the well-known BCH applications, their use as adsorbents to remove pollutants are the mostly discussed, although their potential as catalysts or catalyst supports for advanced (electro)catalytic processes has not been comprehensively explored. In this review, the production/activation/functionalization of metal-supported biochar (M-BCH) are scrutinized, giving special emphasis to the metal-functionalized biochar-based (electro)catalysts as promising catalysts for bioenergy and bioproducts production. Their performance in the fields of biorefinery processes, and energy storage and conversion as electrode materials for oxygen and hydrogen evolutions, oxygen reduction, and supercapacitors, are also reviewed and discussed.

The smart assembly of Co-containing polyoxometalates (POMs) and Co-based zeolitic imidazole frameworks (ZIF-67) is a promising tool to produce active electrocatalysts for the oxygen evolution reaction (OER). The encapsulation of SiW₁₁Co inside ZIF-67 cavities via ‘in situ’ synthesis produced two novel POM@ZIF-67 nanocomposites with low and high POM loadings—SiW₁₁Co@ZIF-67 and SiW₁₁Co[h]@ZIF-67, respectively. Other materials involving the analogue tri-substituted silicotungstate, SiW₉Co₃@ZIF-67 and SiW₉Co₃[h]@ZIF-67, have been prepared for comparison reasons. Regardless of the POM substitution degree, we demonstrated that the bidirectional synergistic POM-ZIF-67 interaction found for the already reported material, SiW₉Co₃@ZIF-67, is applicable to the other first-time prepared nanocomposites. Remarkably, this synergy is radically enhanced in the case of the two high POM loading samples, with these nanostructured materials being very active OER electrocatalysts, exhibiting 150–160 mV decreased overpotentials and much faster kinetics (∼35% decreased Tafel slopes) in relation to pristine ZIF-67. Moreover, they reveal intrinsic OER activities higher than those developed by the expensive commercial references (RuO₂ and IrO₂ powders) especially in the case of SiW₉Co₃[h]@ZIF-67. This important electrocatalytic improvement can be related to the higher POM loadings achieved, as well as to the formation of an open defect-enriched phase wrapping the ‘standard’ ZIF-67 framework in these nanomaterials.