Artificial photosynthesis, specifically H2O dissociation for CO2 reduction with solar energy, is regarded as one of the most promising methods for sustainable energy and utilisation of environmental resources. However, a highly efficient conversion still remains extremely challenging. The hydrogenation of CO2 is regarded as the most commercially feasible method, but this method requires either exotic catalysts or high-purity hydrogen and hydrogen storage, which are regarded as an energy-intensive process. Here we report a highly efficient method of H2O dissociation for reducing CO2 into chemicals with Zn powder that produces formic acid with a high yield of approximately 80%, and this reaction is revealed for the first time as an autocatalytic process in which an active intermediate, ZnH− complex, serves as the active hydrogen. The proposed process can assist in developing a new concept for improving artificial photosynthetic efficiency by coupling geochemistry, specifically the metal-based reduction of H2O and CO2, with solar-driven thermochemistry for reducing metal oxide into metal.

CO2 bubbling into electrolytes is widely used for the electrochemical and photoelectrochemical reduction of CO2 as a carbon source. However, the effects of the CO2 bubbling into the electrolytes have rarely been studied and are not clear. The CO2 bubbling into different electrolytes such as KHCO3, K2CO3, KCl, and KOH was investigated in this research. The concentrations of total dissolved carbon (TC), H2CO3* (sum of dissolved CO2 and H2CO3), HCO3 –, and CO3 2– in different solutions before and after bubbling with CO2 until saturation were evaluated. The CO2 bubbling caused the pH of the electrolytes to decrease and affected the existence forms of the dissolved carbonaceous species. After bubbling with CO2, the major form of dissolved CO2 in KHCO3, K2CO3, and KOH was HCO3 –, while H2CO3* was the dominant species in KCl, HCl, and H2O. The ratio of H2CO3*/TC reduces as the concentration of KHCO3 increases, which is possibly the reason for the decrease of CO2 reduction by the solution of high KHCO3 concentration. Furthermore, CO2 partial pressure increasing caused by the CO2 bubbling strongly enhanced the concentration of CO2 in H2O, which is in accordance with Henry’s law.

Formic acid (HCOOH), with a hydrogen capacity of 4.3 wt. %, has attracted increasing interest in the utilization as a promising H 2 carrier. The CO 2 -HCOOH cycle is believed to be a simple and environmental-friendly process for the charge and discharge of H 2 . In this review, we summarize the state-of-the-art technologies and recent results of the heterogeneously catalyzed dehydrogenation of formic acid. Based on these achievements, future outlooks for improving this system for practical applications are proposed.

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La2(MoO4)3 phosphors with various Eu3+ concentrations were prepared via a facile co-precipitation process. The crystal structure and morphology of the phosphors were characterized by means of XRD and field emission scanning electron microscope. The crystal unit cell parameters a, b, and c for the monoclinic phase La2(MoO4)3 were calculated to be 16.989, 11.927, and 16.086 Å, respectively. The average size of the phosphor particles was estimated to be around 88.5 nm. The Huang–Rhys factor was derived from the phonon sideband spectra to be 0.073. The self-generated quenching process of Eu3+ was explained based on Auzel’s model, and the intrinsic radiative transition lifetime for 5D0 level was confirmed to be 0.99 ms. A new approach for calculating the Judd–Ofelt parameters was developed, meanwhile the Judd–Ofelt parameters Ωλ (λ = 2, 4, 6) of Eu3+ in La2(MoO4)3 phosphors were confirmed to be 10.70 × 10−20, 1.07 × 10−20, and 0.56 × 10−20 cm2, respectively. Finally, the optimal doping concentration for achieving maximum emission intensity was confirmed to be 17 mol. % by analyzing the concentration quenching.