If we define metals as materials with electrons that are bound to a lattice, but not to an individual atoms, then there is another (proposed) option for producing metallic H (at least on the sub-lattice level). K.P. Sinha, Ed Storms, and I have all proposed linear defects as a potential source for LENR.
A. Meulenberg, “Pictorial description for LENR in linear defects of a lattice,” ICCF-18, 18th Int. Conf. on Cond. Matter Nuclear Science, Columbia, Missouri, 25/07/2013, J. Condensed Matter Nucl. Sci. 15 (2015), 117-124 If H atoms are inserted into linear defects of a lattice, the 'random' motion of the H2 molecular electrons is constrained. This lateral constraint of the electron motion means that, instead of massive pressures needed to bring H nuclei close enough together to lower the barrier between atoms, the progressive alignment and increasing overlap of the linearized electrons will do the same thing at room temperature. Progressive loading of H into the lattice defect, may produce a phase change in the H sub-lattice, if conditions are right. The proposed conditions are that the lattice structure of the linear defect, while strong enough to compress the lateral motion of the H electrons, does not strongly impose the lattice spacing onto the sub-lattice. The ability of the sub-lattice to alter/reduce its periodic structure means that at some point in the loading process the aligned-H2 molecular structure changes to that of H(n) and thus the local electrons are now bound to the larger molecule, not just to the pairs. If this alignment happens, and if the sub-lattice spacing can shrink, then a feedback mechanism of the electron-reduced Coulomb barrier between protons becomes dominant and cold fusion is initiated. A question of the process is the nature of the Pauli exclusion principle in this formation of H(n). Spin pairing, both between the individual electrons and between pairs, changes the fermi repulsion to bosonic attraction of electron pairs. It is likely that the pairing is spatially (and temporally?) periodic and this periodicity will introduce resonances between the lattice (fixed) and sub-lattice (variable) spacing. These resonances, which depend on lattice, nature of defect, temperature, and loading, could be the critical feature of amplitude in variations of H(n) nuclear spacing and of rates of cold fusion. Andrew M.