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. 2019 Nov 19;9(1):17027.
doi: 10.1038/s41598-019-53501-x.

Graphene Supported Rhodium Nanoparticles for Enhanced Electrocatalytic Hydrogen Evolution Reaction

Affiliations

Graphene Supported Rhodium Nanoparticles for Enhanced Electrocatalytic Hydrogen Evolution Reaction

Ameerunisha Begum et al. Sci Rep. .

Abstract

Current research on catalysts for proton exchange membrane fuel cells (PEMFC) is based on obtaining higher catalytic activity than platinum particle catalysts on porous carbon. In search of a more sustainable catalyst other than platinum for the catalytic conversion of water to hydrogen gas, a series of nanoparticles of transition metals viz., Rh, Co, Fe, Pt and their composites with functionalized graphene such as RhNPs@f-graphene, CoNPs@f-graphene, PtNPs@f-graphene were synthesized and characterized by SEM and TEM techniques. The SEM analysis indicates that the texture of RhNPs@f-graphene resemble the dispersion of water droplets on lotus leaf. TEM analysis indicates that RhNPs of <10 nm diameter are dispersed on the surface of f-graphene. The air-stable NPs and nanocomposites were used as electrocatalyts for conversion of acidic water to hydrogen gas. The composite RhNPs@f-graphene catalyses hydrogen gas evolution from water containing p-toluene sulphonic acid (p-TsOH) at an onset reduction potential, Ep, -0.117 V which is less than that of PtNPs@f-graphene (Ep, -0.380 V) under identical experimental conditions whereas the onset potential of CoNPs@f-graphene was at Ep, -0.97 V and the FeNPs@f-graphene displayed onset potential at Ep, -1.58 V. The pure rhodium nanoparticles, RhNPs also electrocatalyse at Ep, -0.186 V compared with that of PtNPs at Ep, -0.36 V and that of CoNPs at Ep, -0.98 V. The electrocatalytic experiments also indicate that the RhNPs and RhNPs@f-graphene are stable, durable and they can be recycled in several catalytic experiments after washing with water and drying. The results indicate that RhNPs and RhNPs@f-graphene are better nanoelectrocatalysts than PtNPs and the reduction potentials were much higher in other transition metal nanoparticles. The mechanism could involve a hydridic species, Rh-H- followed by interaction with protons to form hydrogen gas.

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Conflict of interest statement

The authors have no competing interests as defined by Nature Publishing Group, or other interests that might be perceived to influence the results and/or discussion reported in this paper.

Figures

Figure 1
Figure 1
H-cluster, the active site. Structure of the Hydrogen-cluster in the H2 evolving bacterium Clostridium pasteurianum.
Figure 2
Figure 2
TEM images of RhNPs and RhNPs@f-graphene. (A) RhNPs at low magnification; (B) RhNPs at high magnification; (C) RhNPs@f-graphene; (D) RhNPs@rGO.
Figure 3
Figure 3
SEM analysis of RhNPs and RhNPs@f-graphene. (A) SEM image of RhNPs with inbox showing aggregation of nanoparticles; (B) SEM image of RhNPs@f-graphene at low magnification; (C) SEM image of RhNPs@f-graphene at higher magnification; (D) EDX analytical result of RhNPs; (E) Powder XRD spectrum of RhNPs; (F) EDX analytical result of RhNPs@f-graphene; (G) Powder XRD spectrum of RhNPs@f-graphene.
Figure 4
Figure 4
TEM images of the composites. (A) TEM image of PtNPs@f-graphene; (B) TEM image of CoNPs@f-graphene; (C) Powder XRD spectrum of PtNPs@f-graphene.
Figure 5
Figure 5
Electrocatalysis by RhNPs. Cyclic voltammograms of RhNPs as a function of increasing concentrations of added p-TsOH (red to olive green) in water. (0.5 M p-TsOH, 0.2 mL each in water). Displaying only forward reduction waves for clarity; scan rate of 100 mVs−1 (Supporting electrolyte, KNO3/H2O (0.2 M), GCE working, Pt wire auxillary and Ag/AgCl reference electrodes).
Figure 6
Figure 6
H2 evolution from acidic water by RhNPs@f-graphene. Cyclic voltammograms of RhNPs@f-graphene as a function of increasing concentrations of added p-TsOH (red to magenta) in water. (0.5 M p-TsOH, 0.2 mL each in water). Displaying only forward reduction waves for clarity; scan rate of 100 mVs−1 (Supporting electrolyte, KNO3/H2O (0.2 M), GCE working, Pt wire auxillary and Ag/AgCl reference electrodes).
Figure 7
Figure 7
H2 evolution from acidic water by f-graphene in the absence of electrocatalysts. Cyclic voltammograms (black to blue) of f-graphene as a function of increasing concentrations of added p-TsOH in water. (0.5 M p-TsOH, 0.2 mL each in water). scan rate of 100 mVs−1 (Supporting electrolyte, KNO3/H2O (0.2 M), GCE working, Pt wire auxillary and Ag/AgCl reference electrodes).
Figure 8
Figure 8
Mechanism of reduction of protons to hydrogen gas on RhNPs@f-graphene. Display of RhNPs on a functionalized graphene layer which take up protons and convert to hydrogen gas.
Figure 9
Figure 9
Comparison of the onset potentials and electrocatalytic efficiency of RhNPs@f-graphene with other transition metal@f-graphene nanocomposites. Cyclic voltammograms of (A) RhNPs: (B) PtNPs; (C) CoNPs; (D) RhNPs@f-graphene; (E) PtNPs@f-graphene; (F) CoNPs@f-graphene as a function of increasing concentrations of added p-TsOH in water. (0.5 M p-TsOH, 0.2 mL each in water); (G) Comparison of reduction on-set potentials. black, onset potential for RhNPs@f-graphene, red, on-set potential for PtNPs@-graphene, Blue, onset potential for RhNPs. Displaying only forward reduction waves for clarity; scan rate of 100 mVs−1 (Supporting electrolyte, KNO3/H2O (0.2 M), GCE working, Pt wire auxillary and Ag/AgCl reference electrodes).

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