We study the 2 nm NiFe alloy sample stability by chronoamperometric (CA) test under constant bias of 1.09 V vs. RHE, with an initial current density of ca. 15 mA cm -2 . Figure . 4e reports the long-term performance results. The 2 nm NiFe sample retains more than 100% of the initial current over 40 hours of continuous working, and the current density rises above the initial current density value (j/j 0 >100%) at around 5 h testing. We then conduct accelerated CA tests at the intensive PEC working condition with a constant bias of 1.80 V vs. RHE, with an initial current density over 30 mA cm -2 . The photoanode operates for over 250 hours with above 88% remaining of the initial current density (Fig. ). Figure visualizes long-term stability and ABPE efficiency value of n-Si/SiO x /TiO x /NiFe oxyhydroxides-alloy photoanodes against the state-of-the-art with efficiency above 1% (details in Table S1 ).