Hydrogen Evolution Reaction Property in Alkaline Solution of Molybdenum Disulfide Modified by Surface Anchor of Nickel–Phosphorus Coating

Terbium- and samarium-doped Li2ZrO3 perovskite materials as efficient and stable electrocatalysts for alkaline hydrogen evolution reactions

The preparation of highly active, rare earth, non-platinum-based catalysts for hydrogen evolution reactions (HER) in alkaline solutions would be useful in realizing green hydrogen production technology. Perovskite oxides are generally regarded as low-active HER catalysts, owing to their unsuitable hydrogen adsorption and water dissociation. In this article, we report on the synthesis of Li2ZrO3 perovskites substituted with samarium and terbium cations at A-sites for the HER. LSmZrO3 (LSmZO) and LTbZrO3 (LTbZO) perovskite oxides are more affordable materials, starting materials in abundance, environmentally friendly due to reduced usage of precious metal and moreover have potential for several sustainable synthesis methods compared to commercial Pt/C. The surface and elemental composition of the prepared materials have been confirmed by X-ray photoelectron spectroscopy (XPS). The morphology and composition analyses of the LSmZO and LTbZO catalysts showed spherical and regular particles, respectively. The electrochemical measurements were used to study the catalytic performance of the prepared catalyst for hydrogen evolution reactions in an alkaline solution. LTbZO generated 2.52 mmol/g/h hydrogen, whereas LSmZO produced 3.34 mmol/g/h hydrogen using chronoamperometry. This was supported by the fact that the HER electrocatalysts exhibited a Tafel slope of less than 120 mV/dec in a 1.0 M alkaline solution. A current density of 10 mA/cm2 is achieved at a potential of less than 505 mV. The hydrogen production rate of LTbZO was only 58.55%, whereas LSmZO had a higher Faradaic efficiency of 97.65%. The EIS results demonstrated that HER was highly beneficial to both electrocatalysts due to the relatively small charge transfer resistance and higher capacitance values.

Origin of Electrocatalytic Activity in Amorphous Nickel-Metalloid Electrodeposits

In transition metal-based alloys, the nonlinearity of the current at large cathodic potentials reduces the credibility of the linear Tafel slopes for the evaluation of electrocatalytic hydrogen activity. High-precision nonlinear fitting at low current densities describing the kinetics of electrochemical reactions due to charge transfer can overcome this challenge. To show its effectiveness, we introduce a glassy alloy with a highly asymmetric energy barrier: amorphous NiP electrocoatings (with different C and O inclusions) via changing the applied DC and pulsed current and NaH₂PO₂ content. The highest hydrogen evolution reaction (HER) activity with the lowest cathodic transfer coefficient α = 0.130 with high J₀ = -1.07 mA cm^-2 and the largest surface areas without any porosity are observed for the pulsed current deposition. The calculated α has a direct relation with morphology, composition, chemical state and coating thickness defined by the electrodeposition conditions. Here, a general evaluation criterion with practicality in assessment and high accuracy for electrocatalytic reactions applicable to different metallic alloy systems is presented.