Bing K. Liu

Natural photosynthesis is usually recognized as an efficient mechanism to achieve solar energy conversion. We construct a CdS/WO3 nanojunction achieving a Z-scheme for clean hydrogen fuel evolution by mimicking the natural photosynthesis. Although WO3 alone cannot be used for H2 evolution from water splitting, it can significantly increase the H2 evolution activity of CdS through a Z-scheme mechanism with lactate as electron donor. The CdS/WO3 photocatalyst has a high H2 evolution rate of 369 μmol g–1 h–1 at a CdS concentration of 20 wt %, which is 5 times as high as that of CdS with lactic acid as electron donor. For further improving the hydrogen production rate, we introduce the noble metal Pt to ameliorate the charge transport between CdS and WO3. Good H2 evolution rates up to 2900 μmol g–1 h–1 were obtained with WPC3, which is about 7.9 times the rate of WC20 with visible radiation. The interesting thing is that the photocatalytic mechanism of CdS/WO3 is different from the previously reported mechanism. The results of TPV (transient photovoltage) and SPV (surface photovoltage) indicate that the Z-scheme system of CdS/WO3 can effectively promote charge separation and depress the charges recombining of photogenerated charge in CdS, based on the Z-scheme mechanism, resulting in efficient H2 production activity under visible light.

Cobalt hydroxide/cadmium sulfide composite was prepared using an easy coprecipitation strategy. The field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) confirmed that Co(OH)2 nanometer particles were modified on CdS. Even without noble-metal cocatalyst, the photocatalytic H2 evolution over CdS after Co(OH)2 loaded was evidently increased. The most excellent Co(OH)2 of 6.8 mol %, resulted in a H2 generation rate of 61 μmol h(-1) g(-1), which exceeded that of pure CdS by a factor of 41 times. Surface photovoltage (SPV) and surface photocurrent (SPC) investigations revealed that the photogenerated electrons could be captured by the loaded Co(OH)2 nanoparticles. The interface formed between Co(OH)2 and CdS is vital to the enhancement of photocatalytic H2 generation. Electrochemical measurement results indicated that another reason for the enhanced photocatalytic activity of Co(OH)2/CdS catalyst is that Co(OH)2 has outstanding H2 generation activity.