AbstractLaterally large (≈3 µm), atomically thin 2D Bi₂O₂CO₃ nanosheets (2D bismuth oxycarbonate, 2D bismutite) are fabricated via sonochemically assisted, template‐free synthesis. Keys to the synthesis of the freestanding, laterally large 2D Bi₂O₂CO₃ nanosheets from bulk Bi powder are choice of suspension medium, controlled reaction temperatures, and several hours processing time. Lateral sizes of 2D Bi₂O₂CO₃ can be controlled between µm‐sized nanosheets and tens of nm sized nanoflakes solely based on the choice of suspension medium. The here introduced 2D Bi₂O₂CO₃ nano‐sheets/‐flakes are then hybridized by a simple mix‐and‐match approach with TiO₂ nanoparticles for testing in suspension‐type photocatalytic hydrogen production via water splitting. This introduces the 2D Bi₂O₂CO₃ as a prospective noble‐metal‐free catalyst component with TiO₂ for photocatalytic hydrogen evolution, beyond Bi₂O₂CO₃'s current use as photocatalyst for organic pollutant degradation. These results enrich the fabrication toolbox of emerging 2D pnictogen oxycarbonates toward large 2D nanosheets and demonstrate the potential of 2D Bi₂O₂CO₃ as a catalyst component for hydrogen evolution in photocatalytic water splitting.