Enhanced proton and electron reservoir abilities of polyoxometalate grafted on graphene for high-performance hydrogen evolution. Issue 3 (4th January 2016)

• Record Type: Journal Article
• Authors: Liu, Rongji; Zhang, Guangjin; Cao, Hongbin; Zhang, Suojiang; Xie, Yongbing; Haider, Ali; Kortz, Ulrich; Chen, Banghao; Dalal, Naresh S.; Zhao, Yongsheng; Zhi, Linjie; Wu, Cai-Xia; Yan, Li-Kai; Su, Zhongmin; Keita, Bineta
• Is Part Of: Energy & environmental science. Volume 9:Issue 3(2016)
• Page Start: 1012
• Page End: 1023
• Publication Date: 2016-01-04
• Subjects: Energy conversion -- Periodicals; Fuel switching -- Periodicals; Environmental sciences -- Periodicals; Environmental chemistry -- Periodicals; 333.79
• DOI: 10.1039/c5ee03503a
• Languages: English
• ISSNs: 1754-5692

Abstract

Abstract : A 3D configuration of high-quality graphene sheets and a polyoxometalate [H7 P8 W48 O184 ] 33− showing excellent hydrogen evolution activity at extremely low overpotential. Abstract : A beneficial "microenvironment effect" on the efficiency of confined electrocatalysts is predicted by theory. However, examples of its experimental confirmation are scarce for catalysts based on polyoxometalates for the hydrogen evolution reaction (HER). For this purpose, the cyclic 48-tungsto-8-phosphate [H7 P8 W48 O184 ] 33− (P8 W48 ) was fixed in a 3D configuration on reduced graphene oxide sheets (rGO) to boost its HER activity. The HRTEM imaging and the solid state 31 P NMR spectrum of P8 W48 /rGO reveal a strong interaction between individual P8 W48 and transparent rGO sheets. The calculation of the interaction between P8 W48 and graphene (G) sheets is difficult to perform within a reasonable period of time because of the large size and very high overall negative charge of P8 W48 . However, as P8 W48 is symmetrical, a quarter of its structure [H2 P2 W12 O48 ] 12− (P2 W12 ) was extracted as a DFT calculation model. As P8 W48 in P8 W48 /rGO is neutral, due to surrounding counter cations, the calculation model P2 W12 is neutral with protons considering the affordable computational time. The adsorption energy for P2 W12 on G (−1.55 eV) and the charge transfer between P2 W12 and G (0.66 |e|) indicate that a strong interaction between P2 W12 and G sheets exists. Kinetic studies show that the P8 W48 /rGO hybrids display excellent HER activity in acid, further confirmed by reproducible generation of hydrogen with quantitative faradaic yield and a high turnover frequency (11 s −1 at 295 mV overpotential) for a noble metal-free electrocatalyst. Importantly, the overpotentials required for the HER compare well with those of the commercial Pt/C (20 wt% Pt), which indicates that P8 W48 /rGO is a promising cheap HER electrocatalyst. We demonstrate here the most convincing experimental evidence of the "microenvironment effect" on HER electrocatalysis by a polyoxometalate.