Unraveling the Synergy of Anion Modulation on Co Electrocatalysts by Pulsed Laser for Water Splitting: Intermediate Capturing by In Situ/Operando Raman Studies

Abstract

Herein, the authors produce Co‐based (Co3(PO4)2, Co3O4, and Co9S8) electrocatalysts via pulsed laser ablation in liquid (PLAL) to explore the synergy of anion modulation on phase‐selective active sites in the electrocatalytic hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Co3(PO4)2 displays an ultralow overpotential of 230 mV at 10 mA cm−2 with 48.5 mV dec−1 Tafel slope that outperforms the state‐of‐the‐art Ir/C in OER due to its high intrinsic activity. Meanwhile, Co9S8 exhibits the highest HER performance known to the authors among the synthesized Co‐based catalysts, showing the lowest overpotential of 361 mV at 10 mA cm−2 with 95.8 mV dec−1 Tafel slope in the alkaline medium and producing H2 gas with ≈500 mmol g−1 h−1 yield rate under −0.45 V versus RHE. The identified surface reactive intermediates over in situ electrochemical–Raman spectroscopy reveal that cobalt(hydr)oxides with higher oxidation states of Co‐cation forming under oxidizing potentials on the electrode–electrolyte surface of Co3(PO4)2 facilitate the OER, while Co(OH)2 facilitate the HER. Notably, the fabricated two‐electrode electrolyzers using Co3(PO4)2, Co3O4, and Co9S8 electrocatalysts deliver the cell potentials ≈2.01, 2.11, and 1.89 V, respectively, at 10 mA cm−2. This work not only shows PLAL‐synthesized electrocatalysts as promising candidates for water splitting, but also provides an underlying principle for advanced energy‐conversion catalysts and beyond.

CoFe layered double hydroxides with adjustable composition and structure for enhanced oxygen evolution reaction

“…4a). In detail, Co LDH showed strong peaks at 464 cm À1 and 532 cm À1 , which can be assigned to the E g vibration mode of Co-O-H. 50,51 For Fe LDH, the peak at 684 cm À1 corresponded to the E g vibration mode of Fe-O-H. The peak at 1079 cm À1 in Co LDH and that at 1294 cm À1 in Fe LDH corresponded to CO 3 2À .…”

Architecting the High‐Entropy Oxides on 2D MXene Nanosheets by Rapid Microwave‐Heating Strategy with Robust Photoelectrochemical Oxygen Evolution Performance

“…The peaks at 778.8 and 794.3 eV corresponded to Co 2+ , and those at 780.8 and 795.9 eV were assigned to Co 3+ . [ 30,56 ] For the Fe 2p spectrum (Figure 3d), two pairs of Fe 2p 3/2 and Fe 2p 1/2 doublets with their satellite peaks were observed. The peaks at 171.1 and 721.8 eV belonged to Fe 2+ ; those at 713.9 and 724.1 eV belonged to Fe 3+ .…”

Modulating the Combinatorial Target Power of MgSnN2 via RF Magnetron Sputtering for Enhanced Optoelectronic Performance: Mechanistic Insights from DFT Studies

“…We determined the full width at half maximum (fwhm) of the (120) diffraction peaks and used the Scherrer equation (eq ) to calculate the crystalline size because the growth orientation of this peak was the most evident. D = 0.9 λ β .25em nobreak0em0.25em⁢ cos nobreak0em.25em⁡ θ where λ denotes the wavelength of the X-ray, the fwhm is represented by β, and θ is the incident angle. − The crystallite size increased as the Sn power density increased from 0.24 to 0.74 W/cm 2 (Table ). An increase in argon-ion flux caused by high Sn power density had a profoundly energetic effect on the Sn target.…”

“…Incident monochromatic light was used in Raman spectroscopy to observe the vibrational modes of the thin MgSnN 2 film samples. Owing to inelastic scattering regarding the incident frequency, the Raman scattered light experienced a frequency shift to a low or high frequency. , Thus, depending on the vibrational modes of the sample, the energy of a laser shifts up or down when it interacts with molecular vibrations. Figure S2 shows the graph of the vibrational Raman spectra for the MgSnN 2 thin films fabricated at various Sn power densities by RF sputtering.…”