Electrocatalytic Hydrogen Evolution Reaction on Reduced Graphene Oxide Electrode Decorated with Cobaltphthalocyanine

Electrocatalytic Hydrogen Evolution Reaction on Reduced Graphene Oxide Electrode Decorated with Cobaltphthalocyanine

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Abstract and figures:

Electrocatalytic hydrogen evolution reaction (HER) on azido graphene oxide (GO-N3) and reduced azido graphene oxide (RGO-N3) electrodes decorated with the cobaltphthalocyanine complex bearing terminal alkyne moieties (TA-CoPc) was investigated. GCE/RGO-N3 electrode was constructed with the electrochemical reduction of GO-N3 coated on a glassy carbon electrode. Decoration of GCE/RGO-N3 and GCE/GO-N3 electrodes were performed with a new electrode modification technique, “click electrochemistry (CEC)”, with which TA-CoPc complex was bonded to azido functional groups of GO-N3 and RGO-N3 on the electrodes. The modified GCE/RGO-N3/TA-CoPc and GCE/GO-N3/TA-CoPc electrodes were characterized with square wave voltammetry and electrochemical impedance spectroscopy (EIS), and then tested as heterogeneous electrocatalysts for HER. GCE/RGON3/TA-CoPc electrode illustrates well electrocatalytic activity by decreasing the over-potential of the bare electrode about 340 mV and increasing the current density of the electrode about 15 fold at low pHs with absolutely high stability and reproducibility.

SUBJECT: Electrocatalyst, Hydrogen evolution reaction, Phthalocyanine, Click electrochemistry, Graphene Oxide, Reduced graphene oxide

Scheme 1. Synthetic pathways for the phthalonitriles and phthalocyanines (i) CoCl2, DBU, n-pentanol, heat, N2.

Scheme 2. Electrode modification via the “click chemistry” (CC) and the “click electrochemistry” (CEC) between GO-N3, RGO-N3, and TA-CoPc

 

Fig. 1. (a) FTIR spectra of GO and GO-N3. b) EDX of GO-N3.

 

Fig. 2. Repetitive CV responses of GCE/GO-N3 electrode at 100 mV s−1 scan rate in LiClO4/H2O electrolyte system.

 

Fig. 3. SWVs of GCE/GO-N3, GCE/RGO-N3, GCE/GO-N3/TA-CoPc, and GCE/RGO-N3/TA-CoPc electrodes recorded at 100 mV s−1 scan rate in PBS containing 0.1 M LiClO4.

 

Fig. 4. EISs of GCE/GO-N3, GCE/RGON3, GCE/GO-N3/TA-CoPc, and GCE/RGO-N3/TA-CoPc electrodes recorded in [Fe(CN)6]3−/[Fe(CN)6]4− aqueous solution.

 

Fig. 5. LSVs of GCE/GO-N3, GCE/RGO-N3, GCE/GO-N3/TA-CoPc, and GCE/RGO-N3/TA-CoPc electrodes recorded at 0.010 mV s−1 scan rate with 1000 rpm rotating speed in PBS containing 0.1 M LiClO4. (a) pH 3.40; (b) pH 5.60; (c) pH 7.40; (d) pH 10.00. (pHs of the electrolyte was adjusted with conjugated acid of the buffer solution).

Table 1. Analysis of LSV and CA and CC responses of the bare and modified electrodes during HER measurements.

Electrodes pHs of the electrolytes
3.40 5.60 7.40 10.0
GCE/GO-N3 ΔE/mVa 80 40 48 80
J (m)/J(b)b 2.40 1.7 2.3 2.6
Q(m)/Q(b)c 1.8 1.3 1.7 1.2
βc (mV dec−1)d 139 128 136 147
GCE/RGO-N3 ΔE/mVa 130 42 50 110
J (m)/J(b)b 4.1 1.8 3.1 2.7
Q(m)/Q(b)c 3.1 1.6 1.9 1.4
βc (mV dec−1)d 91 105 117 106
GCE/GO-N3/TA-CoPc ΔE/mVa 240 300 320 300
J (m)/J(b)b 9.2 7.5 7.2 6.2
Q(m)/Q(b)c 4.8 2.2 2.2 2.5
βc (mV dec−1)d 121 138 145 135
GCE/RGO-N3/TA-CoPc ΔE/mVa 340 320 380 310
J (m)/J(b)b 15.0 10.5 13.3 9.3
Q(m)/Q(b)c 6.6 2.7 3.5 4.2
βc (mV dec−1)d 131 120 137 140
a

ΔE/mV: onset potential differences between modified and bare electrodes measured during LSV analysis of HER.

b

J (m)/J(b): ratio of the current densities of HER on modified and bare electrodes recorded with LSVs at the final potentials.

c

Q(m)/Q(b): ratio of the charge densities of HER on modified and bare electrodes recorded with CCs.

d

βc (mV): Tafel slopes derived from LSVs.

 

Fig. 8. CCs of GCE/GO-N3, GCE/RGO-N3, GCE/GO-N3/TA-CoPc, and GCE/RGO-N3/TA-CoPc electrodes recorded at 0.010 mV s−1 scan rate with 1000 rpm rotating speed in PBS containing 0.1 M LiClO4. (a) pH 3.40; (b) pH 5.60; (c) pH 7.40; (d) pH 10.00. (pHs of the electrolyte was adjusted with conjugated acid of the buffer solution).

 

Fig. 9. (a) CA and (b) CCs of GCE/GO-N3, GCE/RGO-N3, GCE/GO-N3/TA-CoPc, and GCE/RGON3/TA-CoPc electrodes recorded at 0.010 mV s−1 scan rate with 1000 rpm rotating speed in PBS containing 0.1 M LiClO4 at pH 3.40 with 60 s excitation.

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