No catalyst addition and highly efficient dissociation of H₂O for the reduction of CO₂ to formic acid with Mn

The "greenhouse effect" caused by the increasing atmospheric CO₂ level is becoming extremely serious, and thus, the reduction of CO₂ emissions has become an extensive, urgent, and long-term task. The dissociation of water for CO₂ reduction with solar energy is regarded as one of the most promising methods for the sustainable development of the environment and energy. However, a high solar-to-fuel efficiency keeps a great challenge. In this work, the first observation of a highly effective, highly selective, and robust system of dissociating water for the reduction of carbon dioxide (CO₂) into formic acid with metallic manganese (Mn) is reported. A considerably high formic acid yield of more than 75% on a carbon basis from NaHCO₃ was achieved with 98% selectivity in the presence of simple commercially available Mn powder without the addition of any catalyst, and the proposed process is exothermic. Thus, this study may provide a promising method for the highly efficient dissociation of water for CO ₂ reduction by combining solar-driven thermochemistry with the reduction of MnO into Mn.