Table 1. A Benchmark of the PEC Performance of Our NiO/n-GaN Photoelectrodes against Other Photoelectrodes Made of NiO-Coated Semiconductors^a.

materials of photoelectrode	deposition method of NiO	electrolyte	light power density (mW/cm2)	photocurrent density (mA/cm2)	H2/HCOOH production rate	ref.
NiO/n-GaN	sol–gel drived	1 M NaCl	600 (Xe lamp)	∼0.9 at 1 V(Ag/AgCl)	15(H2) (μmol/h·cm2)	(16)
NiO/n-GaN	PA-MBE	1 M NaOH	100 (Xe lamp)	0.5–1.2 at 1.2 V(RHE)	N/A	(18)
NiO/n-GaN	diluted MOD	1 M NaOH	500 (Xe lamp)	2.6–3.1 at 0 V(Ag/AgCl)	N/A	(27)
NiO/n-GaN	spin-coated	1 M NaCl	700 (Xe lamp)	∼1.7 at 1.0 V(Ag/AgCl)	N/A	(28)
NiO/Si	thermal annealed Ni	0.5 M Na2SO4	100 (Xe lamp)	∼0.036 at 0 V(Ag/AgCl)	N/A	(29)
NiO/ZnO	electrodeposition	0.5 M Na2SO4	100 (Xe lamp)	1.8 at 1.23 V(RHE)	N/A	(30)
NiO/ZnO–CdS core–shell	chemical bath deposition	0.25 M Na2S and 0.35 M Na2SO3	100 (AM 1.5G)	1.8 at 1.23 V(RHE)	N/A	(31)
NiO/3C-SiC	pulsed-plasma sputtering	1 M NaOH	100 (AM 1.5G)	∼1.0 at 0.55 V(RHE)	27(H2) (μL/h·cm2)	(32)
NiO/n-GaN	RF sputtering	1 M NaCl	800 (Xe lamp)	∼7.0 at 1 V(Ag/AgCl)	30(H2)/100(HCOOH) (μmol/h·cm2)	this work

^aN/A: not available.