Photonic-Chemical Coupling in Confined Catalytic Nanocavities for Selective Energy Conversion

Selective energy conversion in confined catalytic nanocavities is examined through a coupled reactive‑photonic framework rather than only as a microscale flame‑stability problem. The experimental basis combines visible/NIR spectral measurements from Pt‑coated anodic porous alumina (APA) nanocavities with a smooth zirconia reference, together with structural information on ordered nanocavity platforms. Within the measured window, the Pt‑coated APA spectrum departs more strongly from the corresponding grey‑body fit than the zirconia reference, providing direct experimental indication that confinement alters radiative behaviour at accessible wavelengths. We interpret this divergence through a photonic‑chemical coupling framework in which high‑aspect‑ratio cavities reduce access to free‑space long‑wavelength radiative escape while increasing wall‑coupled relaxation and catalytic‑interface interaction. A converged FDTD benchmark at the dominant CO₂-4.3 µm band (Purcell factor Fp ≈ 1.26) shows moderate total LDOS enhancement while aperture flux is suppressed by more than six orders of magnitude relative to total radiated power. This indicates that the cavity redirects the emitted energy into wall‑coupled channels rather than allowing free‑space axial emission. The result is not a full mid‑IR device demonstration, but a mechanistically grounded, computationally supported case that confined combustion in Pt‑coated APA can operate as an integrated selective emitter and wall‑coupled heat‑redistribution architecture relevant to thermophotovoltaic and hybrid TPV/TEG energy conversion.