Hydrogen peroxide (H2O2) is a versatile chemical, valued as both a promising energy carrier and a widely used oxidizing agent in disinfection and organic synthesis. The light-driven catalytic oxygen reduction reaction (ORR) using carbon nitrides (CNx) is based on the conversion of solar into chemical energy and thus offers a sustainable pathway for decentralized H2O2 production. This study presents a novel synthetic strategy for producing ionic derivatives of CNx, specifically poly(heptazine imides) (PHIs) with higher specific surface areas, using an ordered mesoporous silica material (SBA-15) as a template. The templated PHIs exhibit enhanced porosity, controlled incorporation of transition metals, improved visible-light absorption, tunable hydrophilicity and more efficient charge separation compared to bulk CNx. PHIs containing iron, cobalt or nickel accelerate H2O2 decomposition, whereas templated potassium PHI (KPHI) achieves a 2.1-fold increase in H2O2 production with ethanol as a hole scavenger under visible light irradiation (455 nm, 50 mW·cm−2) compared to bulk KPHI (KPHI_b). A high H2O2 production rate of 19.0 mmol·L−1·h−1 (i.e., 76.2 mmol·g−1·h−1) under the same irradiation condition is achieved with KPHI in a 90 vol.% methanol solution and an optimal photonic yield of 12.8% is obtained with KPHI at 365 nm.