Nickel-based oxides and hydroxides are among the most promising oxygen evolution reaction (OER) electrocatalysts for alkaline water electrolysis, yet understanding how admixed elements influence both bulk redox transformations and formation of surface-active intermediates remains challenging. NiOOH is widely recognized as the active phase in alkaline OER, while Raman studies have highlighted the importance of oxygen-related intermediates formed under anodic polarization [1,2]. Here, we investigate the influence of lanthanum incorporation on sol–gel-derived Ni-based oxide/hydroxide powders and corresponding thin films. By combining different characterization techniques with in situ Raman and in situ UV–visible spectroelectrochemistry, correlations between composition, redox evolution, and OER activity are followed, Ni- and Ni/La-based materials containing 2, 5, and 10 mol% La were synthesized and thermally treated at 300 °C. Structural characterization reveals NiO nanocrystallites embedded in a partially amorphous hydrated matrix. The parallel investigation of powders and thin films, prepared from the same Ni- and Ni/La-sols, enables direct comparison between electrocatalytic response and electro-optical redox behavior [3].

Electrochemical measurements in 0.1 M KOH show progressive activation of NiO into the Ni(OH)₂/NiOOH redox pair during cycling, with a strongly concentration-dependent influence of La [4]. Whereas 2 mol% La causes only minor changes, 5 mol% reduces activity through structural rearrangement, while 10 mol% enhances OER performance. In situ Raman spectroelectrochemistry directly follows the anodic formation of NiOOH through the emergence of characteristic bands at 482 and 556 cm⁻¹ and reveals low-intensity features in the 800–1150 cm⁻¹ region associated with oxygen-related surface species formed under OER conditions [1,2]. Complementary in situ UV–visible spectroelectrochemistry performed on thin films tracks potential-dependent coloration during Ni²⁺/Ni³⁺ oxidation [2,3]. Measurements show that lanthanum not only modifies the catalyst structure, but also influences the course of the electrochemical activation and accessibility of redox-active nickel centers. Together, both in situ techniques provide insight into how lanthanum modifies Ni-based electrocatalysts and demonstrate the importance of combining vibrational and optical spectroelectrochemistry to distinguish between bulk redox processes and surface catalytic transformations during OER [3].