Supplementary Material

Details of experiments and computations, results of XRD, SEM, EDS and UV-Vis-NIR absorption spectra at ambient environment, representative Rietveld fitting of XRD patterns, Representative electrochemical impedance spectroscopy, UV-Vis absorption spectra at high pressure, IR reflectance spectra at high pressure, the photograph of photocurrent response device, and photocurrent response of a high-entropy boride at high pressure, low temperature electrical resistance with different pressure, phonon dispersion curves and phonon density of states of the A7 and S structures, the pressure dependence of Raman shift, calculated electronic band structures of the M, A7 and S phase structures, the DOS at the Fermi level derived from the DOS and calculated Tc, the cell parameters and unit cell volumes of samples derived from HP-XRD data.