Microwave-Assisted Synthesis of Co/CoO_x Supported on Earth-Abundant Coal-Derived Carbon for Electrocatalysis of Oxygen Evolution

Abstract

The evident demand for hydrogen as the ultimate energy fuel for posterity calls for the development of low-cost, efficient and stable electrocatalysts for water splitting. Herein, we report the synthesis of Co/CoO x supported on coal-derived N-doped carbon via a simple microwave-assisted method and demonstrate its application as an efficient catalyst for the oxygen evolution reaction (OER). With the optimal amount of cobalt introduced into the N-doped coal-derived, the developed catalyst achieved overpotentials of 0.370 and 0.429 V during water oxidation at current densities of 1 mA cm −2 and 10 mA cm −2 , respectively. There was no noticeable loss in the activity of the catalyst during continuous galvanostatic polarization at a current density of 10 mA cm −2 for a test period of 66 h. The synergistic interaction of the Co/CoO x moieties with the pyridinic and pyrollic nitrogen functional groups in the N-doped carbon, as well with the other heteroatoms species in the pristine coal favored enhancement of the OER electrocatalytic performance.

Trace metals dramatically boost oxygen electrocatalysis of N-doped coal-derived carbon for zinc–air batteries

“…Upon introduction of trace metals prior to the pyrolysis, the intensity ratio of D-to-G-bands slightly decreased. This is due to the decomposition of unstable volatiles generated from the PC carbon matrix catalyzed by the trace metals during the thermal treatment [25,38] . However, no clear peak shifts or line broadening of the G-and D-bands was observed, indicating that the properties of the carbon structure remained apparently unchanged after the doping [39] .…”

“…The 2D-band (2680 cm -1 ) and (D + G)-band (2920 cm -1 ), which originate from the crystalline graphitic domains and structural disorder or defects, respectively, could be seen for the trace metal-containing NPCC samples. This suggests that stronger structural distortion of the aromatic graphitic carbon domains took place when trace metals were introduced into NPCC [25,26,40,41] .…”

“…A Tafel slope of ca. 60 mV dec −1 usually suggests that a chemical step after the first electron transfer is rate limiting, while a Tafel slope close to 40 mV dec −1 means that the second electron transfer step of the OER determines the reaction rate [25] . We note that the Fe-NPCC and Al-NPCC had the smallest Tafel slopes of 36 and 35 mV dec -1 , respectively, demonstrating superior OER kinetics compared to the other electrocatalysts.…”

“…Nagai et al reported the use of coal as a raw material to prepare electrocatalysts for the ORR in acidic media [20][21][22][23] . We have also reported the feasibility to convert coal into promising ORR, OER and bifunctional ORR/OER electrocatalysts in alkaline media [11,[24][25][26] . It was previously demonstrated that coal can be directly modified into ORR, OER or bifunctional ORR/OER active catalysts without prior purification.…”

Electrochemical efficacies of coal derived nanocarbons

“…For instance, heteroatom modified carbon matrix for enhanced oxygen evolution reaction (OER) activity was developed from brown coal by Pan et al (2019). When an optimum amount of transition metal element (Co) was added to the Nitrogen doped carbon, tendency of nanoparticles to agglomerate was negated and kinetic phenomenon was enhanced.…”