Table 2.
Summary of major oxygen‐deficient Co‐based TMO electrocatalysis for HER and HER/OER.[a]
|
Synthesis method |
Material |
Method |
Overpotential (b.t.) [mV] |
Overpotential (a.t.) [mV] |
Tafel slope (b.t.) [mV dec−1] |
Tafel slope (a.t.) [mV dec−1] |
Ref. |
|---|---|---|---|---|---|---|---|
|
hydrogen treatment |
Co/Co3O4 core–shell nanosheets |
pristine Co/Co3O4 core–shell nanosheets were annealed in H2 at 150, 200, and 300 °C for 3 h |
302 at 20 mA cm−2 |
129 at 20 mA cm−2 |
49 |
44 |
[42] |
|
thermal treatment |
NiCo2O4 nanowire arrays |
a precursor grown on carbon paper [prepared by hydrothermal treatment of a solution containing CoCl2 ⋅ 6H2O, NiCl2 ⋅ 6H2O, and CO(NH2)2] was annealed under air and Ar atmospheres at 350 °C for 2 h |
294 at 10 mA cm−2 |
104 (Ar‐NiCo2O4) 226 (Air‐NiCo2O4) at 10 mA cm−2 |
– |
112 (Ar‐NiCo2O4) 174 (Air‐NiCo2O4) |
[43] |
|
thermal treatment |
Co3O4 nanoflowers |
cobalt alkoxide precursor [obtained by hydrothermally reacting C4H6CoO4 ⋅ 4H2O, poly(N‐vinyl‐2‐pyrrolidone) and ethylene glycol solution (180 °C) for 3 h] was annealed in air (300 °C) |
– |
250 (HER) 297 (OER) at 10 mA cm−2 |
132.8 (HER) 108.4 (OER) |
95.3 (HER) 79.1 (OER) |
[44] |
|
hydrogen treatment |
NF/H‐CoMoO4 nanosheet arrays |
pristine NF/CoMoO4 were annealed in H2/Ar at 400 °C for 1 h |
223 (HER) 330 (OER) at 10 mA cm−2 |
42 (HER) 295 (OER) at 10 mA cm−2 |
117.2 (HER) |
91 (HER) |
[45] |
|
hydrogen treatment |
CoO/MoOx |
pristine CoMoO4 was annealed in H2 at 500 °C for 2 h |
353 (HER) at 10 mA cm−2 370 (OER) at 20 mA cm−2 |
163 (HER) at 10 mA cm−2 310 (OER) at 20 mA cm−2 |
61 (HER) |
44 (HER) |
[46] |
|
plasma treatment |
C−Co3O4 |
pristine Co3O4 nanosheets array was treated by CH4 plasma with different irradiation time (5–30 min), 300 W power 100 Pa |
462 (HER) 340 (OER) at 10 mA cm−2 |
163 (HER) 250 (OER) at 10 mA cm−2 |
128 (HER) 68 (OER) |
89 (HER) 54 (OER) |
[47] |
|
liquid exfoliation |
CoFe LDH‐F |
CoFe LDH was suspended in a flask containing DMF/ethanol; the suspension was vigorously stirred under Ar flow (24 h) |
415 (HER) 345 (OER) at 10 mA cm−2 |
255 (HER) 300 (OER) at 10 mA cm−2 |
116 (HER) 47 (OER) |
95 (HER) 40 (OER) |
[48] |
|
hydro‐thermal treatment |
P‐doped Co3O4 nanosheet |
pristine Co3O4/NF and NaH2PO2 with different weights (20, 60, 100, 140 mg) were heated at 300 °C for 0.5 h |
165 (HER) at 10 mA cm−2 315 (OER) at 20 mA cm−2 |
97 (HER) at 10 mA cm−2 260 (OER) at 20 mA cm−2 |
129 (HER) 85 (OER) |
86 (HER) 60 (OER) |
[49] |
|
plasma treatment |
P‐Co3O4 nanosheet |
NaH2PO2 and pristine Co3O4 were treated with Ar plasma at irradiation times 0–30 min at 200 W and 150 Pa |
460 (HER) 340 (OER) at 10 mA cm−2 |
120 (HER) 280 (OER) at 10 mA cm−2 |
148 (HER) 70.8 (OER) |
52 (HER) 51.6 (OER) |
[50] |
|
thermal treatment |
CuCo2O4@carbon quantum dots |
CuCo precursors [obtained via hydrothermal synthesis via reaction of carbon quantum dots, Cu(NO3)2 ⋅ 3H2O, Co(NO3)2 ⋅ 6H2O, and urea solution at 150 °C for 6 h] were annealed in Ar at 400 °C for 1 h |
467 (OER) 420 (OER) at 10 mA cm−2 |
331 (HER) 290 (OER) at 10 mA cm−2 |
83 (HER) 90.3 (OER) |
65 (HER) 64 (OER) |
[51] |
[a] All reactions performed in alkaline media (1 m KOH). b.t.=before treatment; a.t.=after treatment.