Laser-induced periodic surface structured electrodes with 45% energy saving in electrochemical fuel generation through field localization

Electrochemical oxidation/reduction of radicals is a green and environmentally friendly approach to generating fuels. These reactions, however, suffer from sluggish kinetics due to a low local concentration of radicals around the electrocatalyst. A large applied electrode potential can enhance the fuel generation efficiency via enhancing the radical concentration around the electrocatalyst sites, but this comes at the cost of electricity. Here, we report about a ~45% saving in energy to achieve an electrochemical hydrogen generation rate of 3×1016 molecules cm–2s–1 (current density: 10 mA/cm2) through localized electric field-induced enhancement in the reagent concentration (LEFIRC) at laser-induced periodic surface structured (LIPSS) electrodes. The finite element model is used to simulate the spatial distribution of the electric field to understand the effects of LIPSS geometric parameters in field localization. When the LIPSS patterned electrodes are used as substrates to support Pt/C and RuO2 electrocatalysts, the η10 overpotentials for HER and OER are decreased by 40.4 and 25%, respectively. Moreover, the capability of the LIPSS-patterned electrodes to operate at significantly reduced energy is also demonstrated in a range of electrolytes, including alkaline, acidic, neutral, and seawater. Importantly, when two LIPSS patterned electrodes were assembled as the anode and cathode into a cell, it requires 330 mVs of lower electric potential with enhanced stability over a similar cell made of pristine electrodes to drive a current density of 10 mA/cm2. This work demonstrates a physical and versatile approach of electrode surface patterning to boost electrocatalytic fuel generation performance and can be applied to any metal and semiconductor catalysts for a range of electrochemical reactions

Rapid fabrication of CuMoO4 nanocomposites via electric field assisted pulsed-laser ablation in liquids for electrochemical hydrogen generation

Transition–metal-doped electrocatalysts are considered as low-cost alternatives of Pt and RuO2 electrocatalysts for large scale electrochemical generations of hydrogen and oxygen, respectively. Although, chemical synthesis, typically adopted to produce these electrocatalysts, is scalable but hazardous by-products and chemical wastes create growing environmental concerns. Here, we developed a single step, single pot, and environmentally friendly physical approach of electric field-assisted pulsed laser ablation in liquid for the synthesis of colloidal solution of pure CuMoO4 (CMO) electrocatalysts. The entire process took few minutes and did not involve or generate any chemical. A pulsed picosecond laser was used to ablate MoS2 target at the solid-liquid interface to generate spatially confined plasma plume. Two parallel electrodes (copper sheets) were mounted around the plasma plume to modulate the plasma parameters, control the reactions at the plasma-liquid interface, and simultaneously inject copper ions from the electrode to the laser-produced plasma (LPP) for the generation of CMO. nanoparticles. Surprisingly, we observed that by varying the applied electric field, we can efficiently control the size, shape, crystallinity, morphology, and composition of as produced CMO nanocomposites and enhance their hydrogen evolution reaction (HER) performance. The characterization results proves that the introduction of applied electric field during the laser ablation process significantly change the morphology of as-prepared nanomaterials, and the shape of these nanomaterials were spherical, spindle and cuboid for MoS2, CuO and CMO respectively. Among all the fabricated electrocatalysts, CMO-60 is the best HER performer in alkaline medium, while MoS2 and CuO nanoparticles were the worse. For CMO-60 sample, only 440 mV overpotential required to reach the current density of 10 mA/cm2 and as well as posess good stability. We found that electrocatalysts produced at a higher electric field have higher contents of copper and oxygen leading to a superior HER activity. The developed approach can be applied for the synthesis of other electrocatalysts for a range of chemical reactions

Efficient Recovery of Lithium Cobaltate from Spent Lithium-Ion Batteries for Oxygen Evolution Reaction

Owing to technological advancements and the ever-increasing population, the search for renewable energy resources has increased. One such attempt at finding effective renewable energy is recycling of lithium-ion batteries and using the recycled material as an electrocatalyst for the oxygen evolution reaction (OER) step in water splitting reactions. In electrocatalysis, the OER plays a crucial role and several electrocatalysts have been investigated to improve the efficiency of O2 gas evolution. Present research involves the use of citric acid coupled with lemon peel extracts for efficient recovery of lithium cobaltate from waste lithium-ion batteries and subsequent use of the recovered cathode material for OER in water splitting. Optimum recovery was achieved at 90 °C within 3 h of treatment with 1.5 M citric acid and 1.5% extract volume. The consequent electrode materials were calcined at 600, 700 and 800 °C and compared to the untreated waste material calcined at 600 °C for OER activity. The treated material recovered and calcined at 600 °C was the best among all of the samples for OER activity. Its average particle size was estimated to be within the 20–100 nm range and required a low overpotential of 0.55 V vs. RHE for the current density to reach 10 mA/cm2 with a Tafel value of 128 mV/dec

A versatile interferometric technique for probing the thermophysical properties of complex fluids

Laser-induced thermocapillary deformation of liquid surfaces has emerged as a promising tool to precisely characterize the thermophysical properties of pure fluids. However, challenges arise for nanofluid (NF) and soft bio-fluid systems where the direct interaction of the laser generates an intriguing interplay between heating, momentum, and scattering forces which can even damage soft biofluids. Here, we report a versatile, pump-probe-based, rapid, and non-contact interferometric technique that resolves interface dynamics of complex fluids with the precision of ~1 nm in thick-film and 150 pm in thin-film regimes below the thermal limit without the use of lock-in or modulated beams. We characterize the thermophysical properties of complex NF in three exclusively different types of configurations. First, when the NF is heated from the bottom through an opaque substrate, we demonstrate that our methodology permits the measurement of thermophysical properties (viscosity, surface tension, and diffusivity) of complex NF and biofluids. Second, in a top illumination configuration, we show a precise characterization of NF by quantitively isolating the competing forces, taking advantage of the different time scales of these forces. Third, we show the measurement of NF confined in a metal cavity, in which the transient thermoelastic deformation of the metal surface provides the properties of the NF as well as thermo-mechanical properties of the metal. Our results reveal how the dissipative nature of the heatwave allows us to investigate thick-film dynamics in the thin-film regime, thereby suggesting a general approach for precision measurements of complex NFs, biofluids, and optofluidic devices

Controlling basal plane sulfur vacancy in water splitting MoSx/NiF electrocatalysts through electric-field-assisted pulsed laser ablation

Summary: Eco-friendly, efficient, and durable electrocatalysts from earth-abundant materials are crucial for water splitting through hydrogen and oxygen generation. However, available methods to fabricate electrocatalysts are either hazardous and time-consuming or require expensive equipment, hindering the large-scale, eco-friendly production of artificial fuels. Here, we present a rapid, single-step method for producing MoSx/NiF electrocatalysts with controlled sulfur-vacancies via electric-field-assisted pulsed laser ablation (EF-PLA) in liquid and in-situ deposition on nickel foam, enabling efficient water splitting. Electric-field parameters efficiently control S-vacancy active sites in electrocatalysts. Higher electric fields yield a MoSx/NiF electrocatalyst with a larger density of S-vacancy sites, suited for HER due to lower Gibbs free energy for H∗ adsorption, while lower electric fields produce an electrocatalyst with lower S-vacancy sites, better suited for OER, as shown by both experimental and theoretical results. The present work opens a horizon in designing high-efficiency catalysts, for a wide range of chemical reactions