Reactive Deposition of Cobalt Electrodes: IV . Alkaline Water Electrolysis

Abstract

The electrochemical activity of reactively deposited cobalt electrodes for H2 and O2 evolution in 7N KOH solutions at room temperature has been studied. For a reactively deposited Co electrode (Co loading: 93 mg/cm2), the measured overpotentials were 0.34 V for H2 evolution and 0.39 V for 02 evolution reactions at 1 A/cm 2, room temperature. For the same electrodes operating at i A]cm 2, 80~ the overpotentials were found to be 0.264 V for H2 evolution and 0.285 V for 02 evolution reactions, respectively. More significantly, the effectiveness factor was as high as 70% for H2 evolution at room temperature. The electrochemical efficiency of the electrodes for both Ha and 02 evolution reactions in alkaline solutions is proportional to the Co loading in the range studied (23-132 mg/cm~). The high performance of the electrodes is due to the unique porous structure produced by reactive deposition, characterized by high surface area and an interlaced network of fine and coarse pores, and to the very high electrical conductivity of the electrodes. Preliminary attempts to further reduce the activation polarization of the electrodes by the use of nickel cobalt sulfide have shown promise.

Are metal-free pristine carbon nanotubes electrocatalytically active?

“…In the case of CNT-7, the impurity content is very high, 9500 ppm, but the activity is negligible, 2.8 mA cm -2 for OER measured at 1.8 V (Fig.3A). Similar results were also obtained on the electrocatalytic activity of metal impurities within CNTs for 25 HER and ORR. This indicates that the electrocatalytic activity of residual metallic impurities only becomes pronounced on CNTs with 2-3 walls, while on MWNTs (probably on SWNTs), the catalytic effect of metallic impurities is much lower.…”

“…10 With the addition of 10 mM KCN in 1M KOH solution, the activity of CNTs for OER is substantially decreased (Fig.1C). 25 For example, in the case of TWNTs, CNT-3, j is ～30 mA cm -2 at 1.8 V for OER, much lower than 56 mA cm -2 measured under identical conditions in the absence of KCN. The onset potential is ～1.67 V, also higher than 1.64 V in the absence of KCN.…”

“…This is largely due to the fact that CNTs are commonly synthesized using metal containing catalysts and inevitably there are significant amount of residual metallic impurities within the CNTs such as Fe, Co, Ni, Mn, etc. 3 Kruusenberg et al studied the electrocatalytic activity of 25 acid-treated single-walled and multi-walled CNTs (SWNTs & MWNTs) in acid solution and found that the acid-treated CNTs are less active catalyst for ORR as compared to as-received CNTs. 4 The same group also indicated that CNTs show a higher activity for ORR in alkaline solutions but the metal impurities 30 only play a minor role in the solution of high pH.…”

Water Oxidation by Co‐Based Oxides with Molecular Properties

“…Electrodeposition of Co hydroxides by cyclic voltammetry was later extensively characterized in alkaline and neutral solutions [18,19]. Tseung and coworkers published an extensive series of reports on reactive galvanostatic deposition of Co oxides [20][21][22][23][24][25][26][27]. The surface morphology of their electrodes [17] showed the same nodules as the initially reported CoCat [1] (see Figure 9.1b).…”

Wasserspaltung mit Cobalt

“…[39,40,170,171] Außerdem besteht ein neuerliches Interesse an festen Metalloxid/hydroxid-(Nano)Materialien als aussichtsreiche Katalysatoren für die Wasseroxidation, möglicherweise auch in photochemischen Systemen. [173,174] Hypochlorit, [175] Persulfat, [175] Perruthenat und Ferrat [174] sowie durch [ [161,[182][183][184][185] oder saurer bis neutraler [186,187] Lösung, kathodische Abscheidung ausgehend von CoCl 2 , [188][189][190][191][192][193][194][195][196] auch in Gegenwart von Acetationen, [197,198] Passivierung einer Cobaltelektrode, [199] chemische Dampfabscheidung [200] oder reaktives "Sputtern" mit O 2 -Plasma [201] ). Auch Co 3 O 4 -Nanowürfel wurden als aktiv beschrieben.…”