Speaking of a potential cross-over area between localized HTSC (high temperature superconductivity) and LENR, consider an important but overlooked ion.
The species known as the trihydrogen cation or protonated molecular hydrogen and denoted here as H3+, is actually the most abundant ion in the physical universe, and possibly the key to one kind of non-nuclear gain in LENR. It is likely to be a formative self-catalyst for hydrogen shrinkage or densification as described by Mills and then by Holmlid. The hydrogen cation is actually more stable than molecular H2 in interstellar space, where net charge can be an advantage but the lifetime in condensed matter could also be greatly extended and sequential, giving the appearance of stability - especially in a situation where Cooper pairs of electrons are also formed. It is reasonable to assume that a formative electron pair would immediately attract 3 protons from certain mobile hydrogenated compounds which have exposed positive charge. Water is one such compound. Mills latest effort involves passing massive electrical currents through water-based gels, so he could be achieving temporary electron-pairing by brute force. But in less intensive situations at low temperature, a Cooper pair of electrons could form and immediately bind to 3 adjacent water molecules in such a way the H3+ cation is surrounded by three hydroxyl radicals with musical chairs valence, with the entire ensemble being neutral but fragile. Following the brief lifetime of such an ensemble, one hydrogen atom emerges as deeply densified in the sense of the Inverted Rydberg state of Miley. In this case the H3+ structure could appear as a Copper pair core with 3 protons in Efimov states around the pair. H3+ can thus be the mystery vector for energy gain in certain situations in condensed matter - which heretofore were thought of as LENR, but are non-nuclear and yet gainful. One does not need to fully subscribe to Mills theory either, as there are similar versions with differing parameters which are more accurate. Mills is apparently having great difficulty taming large electrical current arcing, which in the end (and to his chagrin) -- may be completely unnecessary, if the above described situation with Cooper pairs is accurate. In fact, operating temperatures will probably need to be held in a low and steady range for Cooper pairing but possibly this can be achieved near 100°C.
