Caiwu Liang

Exceptionally high OER & HER performances were achieved by rationally designing the electrode structure of non-noble NiFe materials.

Abstract The slow kinetics of oxygen evolution reaction (OER) causes high power consumption for electrochemical water splitting. Various strategies have been attempted to accelerate the OER rate, but there are few studies on regulating the transport of reactants especially under large current densities when the mass transfer factor dominates the evolution reactions. Herein, Ni x Fe 1– x alloy nanocones arrays (with ≈2 nm surface NiO/NiFe(OH) 2 layer) are adopted to boost the transport of reactants. Finite element analysis suggests that the high‐curvature tips can enhance the local electric field, which induces an order of magnitude higher concentration of hydroxide ions (OH − ) at the active sites and promotes intrinsic OER activity by 67% at 1.5 V. Experimental results show that a fabricated NiFe nanocone array electrode, with optimized alloy composition, has a small overpotential of 190 mV at 10 mA cm −2 and 255 mV at 500 mA cm −2 . When calibrated by electrochemical surface area, the nanocones electrode outperforms the state‐of‐the‐art OER electrocatalysts. The positive effect of the tip‐enhanced local electric field in promoting mass transfer is also confirmed by comparing samples with different tip curvature radii. It is suggested that this local field enhanced OER kinetics is a generic effect to other OER catalysts.

Abstract Developing high‐performance noble metal–free electrodes for efficient water electrolysis for hydrogen production is of paramount importance for future renewable energy resources. However, a grand challenge is to tailor the factors affecting the catalytic electrodes such as morphology, structure, and composition of nonprecious metals. Alloying catalytic metals can lead to a synergistic effect for superior electrocatalytic properties. However, alloy formation in solution at low synthesis temperatures may result in better catalytic properties as compared to those at high temperatures due to the controlled reaction kinetics of nucleation and growth mechanisms. Herein, an aqueous solution–based preparation technology is developed to produce NiMo alloy nanowire arrays. The NiMo alloy shows significantly improved hydrogen evolution reaction (HER) catalytic activity, featured with extremely low overpotentials of 17 and 98 mV at 10 and 400 mA cm −2 , respectively, in an alkaline medium, which are better than most state‐of‐the‐art non‐noble metal–based catalysts and even comparable to platinum‐based electrodes. Analyses indicate that the lattice distortions induced by Mo incorporation, increased interfacial activity by alloy formation, and plenty of MoNi 4 active sites at nanowires surface collectively contribute to remarkably enhanced catalytic activity. This study provides a powerful toolbox for highly efficient nonprecious metal–based electrodes for practical HER application.

Abstract Understanding what controls the reaction rate on iridium-based catalysts is central to designing better electrocatalysts for the water oxidation reaction in proton exchange membrane electrolysers. Here we quantify the densities of redox-active centres and probe their binding strengths on amorphous IrO x and rutile IrO 2 using operando time-resolved optical spectroscopy. We establish a quantitative experimental correlation between the intrinsic reaction rate and the active-state energetics. We find that adsorbed oxygen species, *O, formed at water oxidation potentials, exhibit repulsive adsorbate–adsorbate interactions. Increasing their coverage weakens their binding, thereby promoting O–O bond formation, which is the rate-determining step. These analyses suggest that although amorphous IrO x exhibits a higher geometric current density, the intrinsic reaction rates per active state on IrO x and IrO 2 are comparable at given potentials. Finally, we present a modified volcano plot that elucidates how the intrinsic water oxidation kinetics can be increased by optimizing both the binding energy and the interaction strength between the catalytically active states.