Photocatalytic Dehydrogenation of Formic Acid on CdS Nanorods through Ni and Co Redox Mediation under Mild Conditions

Abstract

Selective release of hydrogen from formic acid (FA) is deemed feasible to solve issues associated with the production and storage of hydrogen. Here, we present a new efficient photocatalytic system consisting of CdS nanorods (NRs), Ni, and Co to liberate hydrogen from FA. The optimized noble-metal-free catalytic system employs Ni/Co as a redox mediator to relay electrons and holes from CdS NRs to the Ni and Co, respectively, which also deters the oxidation of CdS NRs. As a result, a high hydrogen production activity of 32.6 mmol h g from the decomposition of FA was noted. Furthermore, the photocatalytic system exhibits sustained H production rate for 12 h with sequential turnover numbers surpassing 4×10 , 3×10 , and 2×10 for Co-Ni/CdS NRs, Ni/CdS NRs, and CoCl /CdS NRs, respectively.

Homogeneous Molecular Iron Catalysts for Direct Photocatalytic Conversion of Formic Acid to Syngas (CO+H2)

“…Figure S4b shows that pure CdS NRs has stable activity for H 2 evolution for only 6hours.A fter that, the H 2 production rate was significantly decreased and no significant increase was observed for H 2 production after 10 hours.T his poor performance of CdS NRs can be attributed to the fast charge recombination and photocorrosion owing to the photogenerated holes. [28] These results showed that the present photocatalytic system is highly active and robust compared to pure CdS NRs under the same conditions.…”

“…Without the Fe-salen catalyst, ap oor H 2 evolution rate of 34 mmol h À1 was observed owing to the rapid recombination of photogenerated electron-hole pairs.H owever,i nt his case,t he CO evolution rate was higher than the H 2 evolution rate,which could be attributed to the presence of Cd 2+ ions generated by photocorrosion of CdS. [28] These Cd 2+ ions were further reduced to Cd 0 as an active catalyst for CO production. [25] When complex 3 was employed, the H 2 evolution rate increased to 300 mmol h À1 ,p roving that the Fe-salen complex is an efficient catalyst that effectively suppresses charge recombination.…”

“…Furthermore,t he Fe catalyst can also suppress the leaching of Cd ions from CdS. [28] Thus,the H 2 evolution rate is much higher than the CO evolution rate in the presence of the Fe catalyst. Forfurther insight, CO 2 was used to replace the N 2 atmosphere in the photocatalytic system to investigate the enhancement in CO production (inset in Figure 3c).…”

Homogeneous Molecular Iron Catalysts for Direct Photocatalytic Conversion of Formic Acid to Syngas (CO+H2)

“…Without the Fe–salen catalyst, a poor H 2 evolution rate of 34 μmol h −1 was observed owing to the rapid recombination of photogenerated electron‐hole pairs. However, in this case, the CO evolution rate was higher than the H 2 evolution rate, which could be attributed to the presence of Cd 2+ ions generated by photocorrosion of CdS . These Cd 2+ ions were further reduced to Cd 0 as an active catalyst for CO production .…”

“…Besides, the Fe catalyst can also capture electrons from the oxidized formate species, which enhances the possibility of protons being reduced. Furthermore, the Fe catalyst can also suppress the leaching of Cd ions from CdS . Thus, the H 2 evolution rate is much higher than the CO evolution rate in the presence of the Fe catalyst.…”