Rhodium is rare and expensive.
Older palladium supplies contained more rhodium and were evidently much more reliable for LENR
Kidwell et al developed a rhodium/palladium alloy which is very effective.
http://lenr-canr.org/acrobat/ViolanteVrfdetectio.pdf
Rhodium is 100% Rh103.
It has a metastable form which lasts 56 minutes, a long time.. .
Palladium on the other hand has no stable isotopes with metastable forms
To make palladium 106(27%) into palladium107 which does have a metastable isotope
one needs to use neutrons (perhaps supplied by stressed deuterium)
An 'old' palladium contaminated with 1% rhodium would be much better than a 'new' palladium
which has to be cooked with neutrons first to make metastable forms.
At SRI International, the Pd wire they had on hand in 1989 gave excess heat. When it was used up, McKubre and his colleagues ordered more of nominally the same wire from the same company, Johnson-Matthey. The new material did not produce excess heat. It was eventually learned that the two batches of Pd wire had a difference in the concentration of rhodium.
JR Pickens 2016
During the course of this work, it was determined that many sources of palladium used historically in successful Fleischmann–Pons experiments actually came from one producer (Engelhard). ICP-MS analysis for trace impurities on older cathodes indicated a change likely was made in the palladium processing by the supplier [23]. Older cathodes had Al, Rh, and Pt present whereas newer cathodes had Zr, Hf, and Y, but little Rh or Pt. Dominguez/Kidwell2014
The Pd90Rh10 alloy was developed as it was thought the hypothesized processing changes might have been responsible for newer palladium cathodes showing no excess energy (about 100 attempts for us) whereas the success rate claimed for older palladium materials was much higher for other investigators Dominguez/Kidwell .2014
