Good question.

The paper's PDF give clearer, less click-baity information on efficiency:

The applied bias photon-to-current efficiency (ABPE) of the Ni(OH)2/Co3O4/3C-SiC photoanode reached 0.47% at 0.65V vs RHE, which is 15.6 and 1.8 times higher than that of the 3C-SiC and Co3O4/3C-SiC photoanodes, respectively (Figure 4b).

A 8x increase is good progress for that specific technique, but 0.47% is very low efficiency. There's still ways to go.