Electrochemical Investigation of the Hydrogen Evolution Reaction on Electrodeposited Films of Cr(OH)3 and Cr2O3 in Mild Alkaline Solutions

Abstract

The hydrogen evolution reaction (HER) from water reduction is the main cathodic reaction in the sodium chlorate process. The reaction typically takes place on electrodes covered with a Cr(III) oxide-like film formed in situ by reduction of sodium dichromate in order to avoid reduction of hypochlorite and thereby increase the selectivity for the HER. However, the chemical structure of the Cr(III) oxide-like film is still under debate. In the present work, the kinetics of the HER were studied using titanium electrodes covered with electrodeposited Cr(OH) 3 or Cr 2 O 3 , which were characterized by means of scanning electron microscopy (SEM), energydispersive x-ray spectroscopy (EDX), x-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. A clear difference in the morphology of the deposited surfaces was obtained, and the structure could be revealed with Raman spectroscopy. The kinetics for the HER were investigated using potentiodynamic and potentiostatic techniques. The results show that the first electron transfer is rate limiting and that the activity decreases in the order Cr 2 O 3 @Ti > bare Ti > Cr(OH) 3 @Ti. The low activity obtained for Cr(OH) 3 @Ti is discussed in terms of the involvement of structural water in the HER and the slow ligand exchange rate for water in Cr(III) complexes, while the high activity obtained for Cr 2 O 3 @Ti is rationalized by a surface area effect in combination with reduction of surface water and water in solution.

Optimized Nickel-Cobalt and Nickel-Iron Oxide Catalysts for the Hydrogen Evolution Reaction in Alkaline Water Electrolysis

“…The result in Figure 10, in which α ranges from 0.4 through 0.6, are therefore quite reasonable. Similar observations with fractional reaction order have been made for other electrocatalysts for both the hydrogen evolution reaction 14,40,50,51 and the oxygen evolution reaction. 48,49,[52][53][54] The experimental values of Tafel slope in Tables IV and V 44 This may be related to similarities in the state of surface Ni in the oxides and metal when exposed to the ambient air or water.…”

Understanding Selectivity in the Chlorate Process: A Step towards Efficient Hydrogen Production

“…Based on the EDX analysis, a Cr:O ratio of 1:0.75 was obtained for Cr(OH) 3 @Au, which is clearly smaller than the Cr:O ratio of 1:3 expected for Cr(OH) 3 . Metallic Cr has been detected after electrodeposition of Cr(OH) 3 ,, and the interpretation is that Cr metal is formed together with the hydroxide or oxide. XRD was used to detect the presence of metallic Cr, but the diffractograms showed only peaks related to the substrate (Figure S2).…”

“…By increasing the laser power to 0.35 mW, clear signals from the deposited layer could observed, Figure a, with signatures from both Cr(OH) 3 and Cr 2 O 3 . In a recent paper, it was shown that for Cr(OH) 3 @Ti no conversion to the oxide takes place below 0.7 mW . By further increasing the laser power, conversion from Cr(OH) 3 to crystalline Cr 2 O 3 takes place, Figure b, as also shown previously ,…”

“…The influence of deposited chromium oxide/hydroxide on hydrogen evolution was therefore investigated using linear sweep voltammetry. The electrolyte was the same as previously used, i. e. 0.2 M Na 2 SO 4 with pH=11 ,. Linear sweep voltammograms for uncovered and covered surfaces are shown in Figure .…”

“…This is in good agreement with studies on in situ formed films, which have shown that the kinetics for water reduction are delayed on Fe and Pt electrodes, but enhanced on Au ,. Results on ex situ deposited Cr(OH) 3 supported on Ti (Figure b) are also in good agreement with recently published work . The fact that the deposited layer can be more active than the underlying substrate demonstrate that hydrogen evolution takes place on the layer.…”