Structural Changes in RuO₂ during Electrochemical Hydrogen Evolution

Abstract

A comprehensive theoretical study of the X-ray photoelectron shifts for RuO 2 during hydrogen evolution has been performed. The shifts have been calculated using firstprinciples density functional theory and are compared with previous theoretical and experimental results to reconsider the proposed structural changes occurring during hydrogen evolution on RuO 2 . We find that during hydrogen evolution hydrogen enters the rutile RuO 2 lattice and converts oxygen groups into hydroxyl groups and that this process explains the experimentally observed increase in unit cell dimensions as well as observed chemical shifts. Furthermore, carbon contamination is the most likely explanation for a set of peaks previously identified as caused by a new RuO(OH) 2 phase. We find that formation of metallic Ru is just one possible explanation for another peak in the X-ray photoelectron spectrum and that explanations including conversion of RuO 2 into Ru(OH) 3 , or removal of oxygen from Ru active surface sites, also can explain the observed shifts.

Stable Hydrogen Production from Water on an NIR‐Responsive Photocathode under Harsh Conditions

“…However, the photocurrents gradually increased to 0.3 and 2.9 mA cm −2 (at pH 7 and 13) over the span of several hours, and the corresponding half‐cell STH (HC‐STH), which indicates the energy conversion efficiency of a photoelectrode under application of bias voltage in a three‐electrode system, reached 1.7% in the case of pH 13. This significant increase over time has not been observed in past studies using Pt as the HER catalyst, although a similar phenomenon (termed “activation”) has been reported for RuO 2 HER catalysts . After the end of an activation period spanning several hours, the photocurrent showed no clear decrease over time spans longer than 10 h. For the sake of comparison, the current–potential curves for (ZnSe) 0.85 (CIGS) 0.15 ‐based photocathodes modified with Pt or Pt/Mo/Ti are shown in Figure b.…”

“…[35] Karlsson et al concluded that hydrogen enters the RuO 2 crystal lattice during the HER, which results in the formation of hydroxides. [36] The data from PEC trials and the AR-XPS spectra are consistent with these reports and strongly suggest that RuO x H y species play an important role during the HER. Furthermore, the pH dependence of the photocurrent can be explained by the difference in the density of hydroxyl species at the RuO 2 surface at equilibrium.…”

“…Blouin and Guay reported that the HER activity of RuO 2 ‐based electrodes is significantly increased by cathodic polarization due to H‐chemisorption within the RuO 2 layer, resulting in an increase in the number of active sites, and found no evidence of metallic Ru formation . Karlsson et al concluded that hydrogen enters the RuO 2 crystal lattice during the HER, which results in the formation of hydroxides . The data from PEC trials and the AR‐XPS spectra are consistent with these reports and strongly suggest that RuO x H y species play an important role during the HER.…”

“…This significant increase over time has not been observed in past studies using Pt as the HER catalyst, [10,11] although a similar phenomenon (termed "activation") has been reported for RuO 2 HER catalysts. [35,36] After the end of an activation period spanning several hours, the photocurrent showed no clear decrease over time spans longer than 10 h. For the sake of comparison, the current-potential curves for www.advancedsciencenews.com www.small-methods.com decreases in photocurrent, to one tenth of the initial value, over just 1 or 2 h. Even though the thickness of the RuO 2 layers in the specimen used for the PEC trials was controlled to be only 6-10 nm, the layer effectively stabilized the photocathode during the HER at 0.6 V RHE in the highly alkaline electrolyte. Figure 3 presents current-potential curves for the RuO 2 / CdS/(ZnSe) 0.85 (CIGS) 0.15 photocathodes before and after the activation process.…”

Stable reconstruction of the (110) surface and its role in pseudocapacitance of rutile-like RuO2

“…Thus each adsorbed or intercalated hydrogen atom (proton) will induce pseudocapacitance in the cathode material. Despite intense research devoted to the study of hydrogen intercalation in the cathode materials, [22][23][24][25][26][27][28][29] the atomicscale processes are still not clearly understood. One of the main problems is the influence of proton adsorption, because it is difficult to distinguish surface pseudocapacitance (charge stored due to protons intercalation into the material) from double layer capacitance (charge stored due to electrostatic potential between electrode surface and electrolyte).…”