Polyoxometalate‐graphene Electrocatalysts for the Hydrogen Evolution Reaction

• Published in: ChemElectroChem Vol. 5; no. 2; pp. 273 - 283
• Main Authors: Fernandes, Diana M., Araújo, Mariana P., Haider, Ali, Mougharbel, Ali S., Fernandes, António J. S., Kortz, Ulrich, Freire, Cristina
• Format: Journal Article
• Language: English
• Published: Weinheim John Wiley & Sons, Inc 01.01.2018
• Subjects: Acidic oxides; Current density; electrocatalysis; Electrocatalysts; Flakes; Graphene; hydrogen evolution reaction; Hydrogen evolution reactions; Nanocomposites; Nanomaterials; oxidized graphene flakes; Platinum; Polyoxometalates; Polyoxometallates; Tafel slopes
• ISSN: 2196-0216; 2196-0216
• DOI: 10.1002/celc.201701210

Electrocatalytic reduction of water, also known as the hydrogen evolution reaction (HER), may be one of the solutions for a sustainable energy supply in the future, but the current use of precious platinum electrocatalysts is a major drawback, owing to the high cost. So, it is urgent to discover cost‐effective and earth‐abundant materials to replace precious‐metal electrocatalysts in order to make this technology economically viable. Herein, we report the preparation and application of three new nanocomposites based on polyoxometalates (POMs) and reduced oxidized‐graphene flakes (rGF_ox) as HER electrocatalysts (ECs). In highly acidic medium (pH=0.3), the POM@rGF_ox ECs showed similar overpotentials (0.033–0.044 V vs. RHE) for a current density of 10 mA cm−2, and these are very close to the state‐of‐the‐art HER EC, 20 wt% Pt/C (0.024 V). The POM‐based nanocomposites also exhibited excellent exchange current densities (0.65–1.02 mA cm−2) and very low Tafel slopes (0.033–0.041 V dec−1). P5W30@rGF_ox exhibited the best HER metrics and also showed long‐term electrochemical stability, as the overpotential only changed 0.009 V for j=10 mA cm−2 after 1000 linear sweep voltammetry cycles. Besides highlighting POM‐oxidized‐graphene flakes composites as a new class of nanomaterial with several important electrochemical applications, this work also points out that the POM shape, size, charge, and composition (W/P ratio) may play an important role in fine‐tuning the HER activity, and opens new avenues for designing a new set of highly efficient, cost‐effective, and durable non‐precious‐metal HER ECs in acidic medium. POMs for HER: Remarkable electrocatalytic efficiency towards the hydrogen evolution reaction (HER) of polyoxometalate@oxidized graphene flakes hybrids is reported in acidic media. The synergetic effect between them leads to HER activities beyond the state‐of‐art catalyst, with impressive exchange current densities (0.65–1.02 mA cm−2) as well as very low overpotentials (0.033–0.044 V vs. RHE) and Tafel slopes (0.033–0.041 V dec−1).