Applications of phthalocyanines (Pcs) in electrocatalysis—including the oxygen reduction reaction (ORR), the carbon dioxide reduction reaction (CO₂RR), the oxygen evolution reaction (OER), and the hydrogen evolution reaction (HER)—have attracted considerable attention recently. Pcs and their derivatives are more attractive than many other macrocycles as electrocatalysts since, although they are structurally related to natural porphyrin complexes, they offer the advantages of low cost, facile synthesis and good chemical stability. Moreover, their high tailorability and structural diversity mean Pcs have great potential for application in electrochemical devices. Here we review the structure and composition of Pcs, methods of synthesis of Pcs and their analogues, as well as applications of Pc-based heterogeneous electrocatalysts. Optimization strategies for Pc-based materials for electrocatalysis of ORR, CO₂RR, OER and HER are proposed, based on the mechanisms of the different electrochemical reactions. We also discuss the structure/composition–catalytic activity relationships for different Pc materials and Pc-based electrocatalysts in order to identify future practical applications. Finally, future opportunities and challenges in the use of molecular Pcs and Pc derivatives as electrocatalysts are discussed.

Porous carbons were obtained by chemical activation of hydrochar, prepared by hydrothermal carbonization using enzymatic hydrolysis lignin originated from the butanol fermentation of corn straw. The intermediate hydrochar was activated using different KOH/hydrochar weight ratios to evaluate the influence of these ratios on its electrochemical properties. The materials thus prepared exhibited high specific surface areas in the range 1290–1660 m² g⁻¹ mainly attributed to the three-dimensional hierarchical texture made up of abundant micropores, small mesopores and macropores, and high electrical conductivity in the 4.0–5.4 S cm⁻¹ range. Consequently, the samples show high specific capacitance, superior rate performance and outstanding durability in three-electrode and two-electrode systems in 6 M KOH. The as-assembled symmetric supercapacitor in an ionic liquid electrolyte system exhibits a superior energy density of 46.8 W h kg⁻¹ and a value of 22.9 W h kg⁻¹ is maintained even at an ultrahigh power density of 25 400 W kg⁻¹. These materials possessing excellent structural features are an ideal candidate for high performance supercapacitors.