Diamond-Mediated Hydrogen Compression via Formation Volume Reduction

Standard diamond anvil cell (DAC) technology compresses hydrogen samples through externally driven mechanical convergence of two opposing diamond tips, following well-mapped pressure-temperature paths. This paper proposes two related but distinct compression methodologies, both departing from this standard approach. The first is endogenous compression: deliberately trapping hydrogen inside a forming synthetic diamond crystal during high-pressure high-temperature (HPHT) synthesis, using the approximately 20–30% volume reduction of the graphite-to-diamond phase transition as the compression driver. The second is two-stage sequential compression: extracting the HPHT-formed diamond crystal containing trapped H2 as a sealed capsule, then loading that diamond capsule into an external DAC as the sample itself for a second compression stage — with the formed diamond walls transmitting external anvil pressure to the enclosed H2. A continuous variant is also proposed: applying DAC compression progressively and simultaneously during diamond formation, so the H2 experiences a monotonically increasing pressure from HPHT baseline through the full DAC range without decompression between stages. The novel pressure-temperature trajectory of these methodologies may encounter intermediate H2 phases inaccessible by conventional compression paths. Limitations, prior art context, and open research questions are discussed. No experimental data is presented. Priority of the conceptual framework is established by this publication date.