Photocatalytic CO2 Reduction with Dissolved Carbonates and Near-Zero CO2(aq) by Employing Long-Range Proton Transport.

Photocatalytic CO2 reduction (CO2R) in ∼0 mM CO2(aq) concentration is challenging but is relevant for capturing CO2 and achieving a circular carbon economy. Despite recent advances, the interplay between the CO2 catalytic reduction and the oxidative redox processes that are arranged on photocatalyst surfaces with nanometer-scale distances is less studied. Specifically, mechanistic investigation on interdependent processes, including CO2 adsorption, charge separation, long-range chemical transport (∼100 nm distance), and bicarbonate buffer speciation, involved in photocatalysis is urgently needed. Photocatalytic CO2R in ∼0 mM CO2(aq), which has important applications in integrated carbon capture and utilization (CCU), has rarely been studied. Using 0.1 M KHCO3 (aq) of pH 7 but without continuously bubbling CO2, we achieved ∼0.1% solar-to-fuel conversion efficiency for CO production using Ag@CrOx nanoparticles that are supported on a coating-protected GaInP2 photocatalytic panel. CO is produced at ∼100% selectivity with no detectable H2, even with copious protons co-generated nearby. CO2 flux to the Ag@CrOx CO2R sites enhances CO2 adsorption, probed by in situ Raman spectroscopy. CO is produced with local protonation of dissolved inorganic carbon species in a pH as high as 11.5 when using fast electron donors such as ethanol. Isotopic labeling using KH13CO3 was used to confirm the origin of CO from the bicarbonate solution. We then employed COMSOL Multiphysics modeling to simulate the spatial and temporal pH variation and the local concentrations of bicarbonates and CO2(aq). We found that light-driven CO2R and CO2 reactive transport are mutually dependent, which is important for further understanding and manipulating CO2R activity and selectivity. This study enables direct bicarbonate utilization as the source of CO2, thereby achieving CO2 capture and conversion without purifying and feeding gaseous CO2.

Biocement from the ocean: Hybrid microbial-electrochemical mineralization of CO2.

Increasing concentrations of atmospheric CO2 are leading to rising global temperatures and extreme weather events. However, the most prominent method of removing CO2 via direct air capture remains cost-prohibitive. Oceans sequester carbon through several naturally occurring carbon dioxide removal (CDR) processes, one of which includes microorganisms that utilize dissolved inorganic carbon (DIC) in their metabolic processes. Atmospheric CO2 is in dynamic equilibrium with DIC at the ocean's surface. Thus, ocean-based CDR can function to capture carbon from the air indirectly. This work discusses a hybrid method that combines primary CO2 capture via the growth of autotrophic microorganisms (i.e., photosynthetic cyanobacteria) and microbially induced carbonate precipitation. Carbon fixation and carbonate precipitation can be co-optimized using bipolar membrane electrodialysis (BPMED) devices , which generate seawater with an adjustable pH. We examine the scale-up potential for naturally produced bio-carbonate composite material and compare its production with published ocean CDR strategies for reducing anthropogenic CO2 emissions.

Narrowing the Phase Distribution of Quasi-2D Perovskites for Stable Deep-Blue Electroluminescence.

Solution-processed quasi-2D perovskites contain multiple quantum wells with a broad width distribution. Inhomogeneity results in the charge funneling into the smallest bandgap components, which hinders deep-blue emission and accelerates Auger recombination. Here, a synthetic strategy applied to a range of quasi-2D perovskite systems is reported, that significantly narrows the quantum well dispersity. It is shown that the phase distribution in the perovskite film is significantly narrowed with controlled, simultaneous evaporation of solvent and antisolvent. Modulation of film formation kinetics of quasi-2D perovskite enables stable deep-blue electroluminescence with a peak emission wavelength of 466 nm and a narrow linewidth of 14 nm. Light emitting diodes using the perovskite film show a maximum luminance of 280 cd m-2 at an external quantum efficiency of 0.1%. This synthetic approach will serve in producing new materials widening the color gamut of next-generation displays.