Zhou Zhaohui, Han Fengshuang, Guo Liejin, Prezhdo Oleg V
International Research Center for Renewable Energy, State Key Laboratory of Multiphase Flow in Power Engineering, Xi'an Jiaotong University, Xi'an 710049, China and Department of Chemistry, University of Southern California, Los Angeles 90007, USA.
International Research Center for Renewable Energy, State Key Laboratory of Multiphase Flow in Power Engineering, Xi'an Jiaotong University, Xi'an 710049, China.
Phys Chem Chem Phys. 2016 Jun 22;18(25):16862-9. doi: 10.1039/c6cp02599d.
It has been a long time that divergent behaviors were observed in many photocatalytic hydrogen evolution reactions (HER) on CdS and ZnS although the two photocatalysts have similar compositions and structures. For example, CdS itself is inactive and loading of cocatalysts is indispensable to achieve high efficiency of hydrogen evolution, but the reverse is true for ZnS. The underlying reasons are still unclear to date. The Volmer reaction of HER on catalysts is H(+) + e(-) + * → H*, and its free energy (ΔGH* = ΔEH* + ΔEZPE - TΔS + eU; the adsorption energy, zero-point energy, entropy and potential energy are on the right side) is a good theoretical descriptor of the electrocatalytic HER activity from the electrocatalytic HER theory. In this paper, we firstly determined the most stable CdS and ZnS(110) termination under the conditions of photocatalytic HER, i.e., pure (110), by calculating the free energies of three reactions related to H2O dissociation on (110). Then we rationalized these behaviors by calculating the free energy of H* adsorption on pure and Pt loaded CdS and ZnS(110) at different pH. The performance of photocatalytic HER on CdS and ZnS was found to be determined jointly by the free energy of H* adsorption and the conduction band minimum (CBM) of the photocatalysts. On pure (110) with large ΔGH*, the photocatalytic HER is favored on ZnS due to its higher CBM; on Pt loaded (110) with small ΔGH*, the photocatalytic HER is favored on CdS due to its lower CBM. These results well explained the divergent behaviors observed in the photocatalytic HER on CdS and ZnS.
尽管硫化镉（CdS）和硫化锌（ZnS）这两种光催化剂具有相似的组成和结构，但在许多光催化析氢反应（HER）中观察到了不同的行为，这已经有很长时间了。例如，CdS本身没有活性，负载助催化剂对于实现高效析氢是必不可少的，但对于ZnS则相反。迄今为止，其潜在原因仍不清楚。根据电催化析氢理论，HER在催化剂上的Volmer反应为H(+) + e(-) + * → H*，其自由能（ΔGH* = ΔEH* + ΔEZPE - TΔS + eU；吸附能、零点能、熵和势能在等式右侧）是电催化HER活性的一个很好的理论描述符。在本文中，我们首先通过计算与(110)面上水离解相关的三个反应的自由能，确定了光催化HER条件下最稳定的CdS和ZnS(110)端，即纯净的(110)面。然后，我们通过计算不同pH值下纯净的以及负载Pt的CdS和ZnS(110)面上H吸附的自由能，对这些行为进行了合理解释。发现CdS和ZnS上光催化HER的性能是由H吸附的自由能和光催化剂的导带最小值（CBM）共同决定的。在具有较大ΔGH的纯净(110)面上，由于ZnS具有较高的CBM，因此光催化HER更有利于在ZnS上发生；在具有较小ΔGH的负载Pt的(110)面上，由于CdS具有较低的CBM，因此光催化HER更有利于在CdS上发生。这些结果很好地解释了在CdS和ZnS上光催化HER中观察到的不同行为。
