Adaptive Bifunctional Electrocatalyst of Amorphous CoFe Oxide @ 2D Black Phosphorus for Overall Water Splitting

CoFeBP Micro Flowers (MFs) for Highly Efficient Hydrogen Evolution Reaction and Oxygen Evolution Reaction Electrocatalysts

Hydrogen is one of the most promising green energy alternatives due to its high gravimetric energy density, zero-carbon emissions, and other advantages. In this work, a CoFeBP micro-flower (MF) electrocatalyst is fabricated as an advanced water-splitting electrocatalyst by a hydrothermal approach for hydrogen production with the highly efficient hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The fabrication process of the CoFeBP MF electrocatalyst is systematically optimized by thorough investigations on various hydrothermal synthesis and post-annealing parameters. The best optimized CoFeBP MF electrode demonstrates HER/OER overpotentials of 20 mV and 219 mV at 20 mA/cm2. The CoFeBP MFs also exhibit a low 2-electrode (2-E) cell voltage of 1.60 V at 50 mA/cm2, which is comparable to the benchmark electrodes of Pt/C and RuO2. The CoFeBP MFs demonstrate excellent 2-E stability of over 100 h operation under harsh industrial operational conditions at 60 °C in 6 M KOH at a high current density of 1000 mA/cm2. The flower-like morphology can offer a largely increased electrochemical active surface area (ECSA), and systematic post-annealing can lead to improved crystallinity in CoFeBP MFs.

Iron doping and interface engineering on amorphous/crystalline Fe-NixSy heterostructures toward high-stability and kinetically accelerated water splitting

It is very important to develop transition metal-based electrocatalysts with excellent activity, high stability and low-cost for overall water splitting. In this work, the Fe-doped NixSy/NF amorphous/crystalline heterostructure nanoarrays (Fe-NixSy/NF) was synthesized by a simple one-step method. The resulting hierarchically structured nanoarrays offer the advantages of large surface area, high structural void fraction and accessible internal surfaces. These advantages not only furnish additional catalytically active sites, but also enhance the stability of the structure and effectively accelerate mass diffusion and charge transport. Experimental and characterization results indicate that Fe doping increases the electrical conductivity of amorphous/crystalline NixSy/NF, and the NiS-Ni3S2 heterojunctions evoke interfacial charge rearrangement and optimize the adsorption free energy of the intermediates, which allows the catalyst to exhibit low overpotential and superior electrocatalytic activity. Especially, the overpotentials of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) of Fe-NixSy/NF at 10 mA cm-2 in an alkaline environment are 102.4 and 230.5 mV, respectively. When applied as a bifunctional catalyst for overall water splitting, it requires only 1.45 V cell voltage to deliver a current density of 10 mA cm-2, which is preferable to the all-noble metal Pt/C || IrO2 electrocatalyst (1.62 mV @ 10 mA cm-2). In addition, Fe-NixSy/NF has excellent stability, and there is no obvious degradation after 96 h continuous operation at a current density of 100 mA cm-2. This work affords insights into the application of doping strategies and crystalline/amorphous synergistic modulation of the electrocatalytic activity of transition metal-based catalysts in energy conversion systems.

Electrochemical water splitting by a bidirectional electrocatalyst

The presence of efficient energy storage and conversion technologies is essential for the future energy infrastructure. Here, we describe crafting a heterostructure composed of a suitably interlinked CeO2 and polycrystalline Bi2O3 dopant prepared on a reduced graphene oxide (Ce_Bi2O3@rGO) surface. This material exhibits exceptional electrocatalytic hydrogen and oxygen evolution reaction in alkaline water (pH∼14.0) to trigger the full water-splitting cycle as a Janus catalyst. The stepwise catalyst preparation and electrochemical cell assembly for simultaneous hydrogen and oxygen evolution have been narrated. For complete details on the use and execution of this protocol, please refer to Aziz et al. (2022).1.

Selective Ethylene Glycol Oxidation to Formate on Nickel Selenide with Simultaneous Evolution of Hydrogen

There is an urgent need for cost-effective strategies to produce hydrogen from renewable net-zero carbon sources using renewable energies. In this context, the electrochemical hydrogen evolution reaction can be boosted by replacing the oxygen evolution reaction with the oxidation of small organic molecules, such as ethylene glycol (EG). EG is a particularly interesting organic liquid with two hydroxyl groups that can be transformed into a variety of C1 and C2 chemicals, depending on the catalyst and reaction conditions. Here, a catalyst is demonstrated for the selective EG oxidation reaction (EGOR) to formate on nickel selenide. The catalyst nanoparticle (NP) morphology and crystallographic phase are tuned to maximize its performance. The optimized NiS electrocatalyst requires just 1.395 V to drive a current density of 50 mA cm^-2 in 1 m potassium hydroxide (KOH) and 1 m EG. A combination of in situ electrochemical infrared absorption spectroscopy (IRAS) to monitor the electrocatalytic process and ex situ analysis of the electrolyte composition shows the main EGOR product is formate, with a Faradaic efficiency above 80%. Additionally, C2 chemicals such as glycolate and oxalate are detected and quantified as minor products. Density functional theory (DFT) calculations of the reaction process show the glycol-to-oxalate pathway to be favored via the glycolate formation, where the CC bond is broken and further electro-oxidized to formate.

Engineering Lattice Oxygen Activation of Iridium Clusters Stabilized on Amorphous Bimetal Borides Array for Oxygen Evolution Reaction

Developing robust oxygen evolution reaction (OER) catalysts requires significant advances in material design and in-depth understanding for water electrolysis. Herein, we report iridium clusters stabilized surface reconstructed oxyhydroxides on amorphous metal borides array, achieving an ultralow overpotential of 178 mV at 10 mA cm^-2 for OER in alkaline medium. The coupling of iridium clusters induced the formation of high valence cobalt species and Ir-O-Co bridge between iridium and oxyhydroxides at the atomic scale, engineering lattice oxygen activation and non-concerted proton-electron transfer to trigger multiple active sites for intrinsic pH-dependent OER activity. The lattice oxygen oxidation mechanism (LOM) was confirmed by in situ ¹⁸ O isotope labeling mass spectrometry and chemical recognition of negative peroxo-like species. Theoretical simulations reveal that the OER performance on this catalyst is intrinsically dominated by LOM pathway, facilitating the reaction kinetics. This work not only paves an avenue for the rational design of electrocatalysts, but also serves the fundamental insights into the lattice oxygen participation for promising OER application.

Phosphorized CoNi2S4 Yolk-Shell Spheres for Highly Efficient Hydrogen Production via Water and Urea Electrolysis

Exploring earth-abundant electrocatalysts with excellent activity, robust stability, and multiple functions is crucial for electrolytic hydrogen generation. Herein, porous phosphorized CoNi 2 S 4 yolk-shell spheres (P-CoNi 2 S 4 YSSs) are rationally designed and synthesized by a combined hydrothermal sulfidation and gas-phase phosphorization strategy. Benefiting from the strengthened Ni 3+ /Ni 2+ couple, enhanced electric conductivity, and hollow structure, the P-CoNi 2 S 4 YSSs exhibit excellent activity and durability towards hydrogen/oxygen evolution and urea oxidation reactions in alkaline solution, affording low potentials of -0.135 V, 1.512 V, and 1.306 V (versus reversible hydrogen electrode) at 10 mA cm -2 , respectively. Remarkably, when used as the anode and cathode simultaneously, the P-CoNi 2 S 4 catalyst merely requires a cell voltage of 1.544 V in water splitting and 1.402 V in urea electrolysis to attain 10 mA cm -2 with excellent durability for 100 h, outperforming most of the reported nickel-based sulfides and even noble-metal-based electrocatalysts. This work therefore not only promotes the application of sulfides in electrochemical hydrogen production but also provides a feasible approach for urea-rich wastewater treatment.

Exclusive Strain Effect Boosts Overall Water Splitting in PdCu/Ir Core/Shell Nanocrystals

Core/shell nanocatalysts are a class of promising materials, which achieve the enhanced catalytic activities through the synergy between ligand effect and strain effect. However, it has been challenging to disentangle the contributions from the two effects, which hinders the rational design of superior core/shell nanocatalysts. Herein, we report precise synthesis of PdCu/Ir core/shell nanocrystals, which can significantly boost oxygen evolution reaction (OER) via the exclusive strain effect. The heteroepitaxial coating of four Ir atomic layers onto PdCu nanoparticle gives a relatively thick Ir shell eliminating the ligand effect, but creates a compressive strain of ca. 3.60%. The strained PdCu/Ir catalysts can deliver a low OER overpotential and a high mass activity. Density functional theory (DFT) calculations reveal that the compressive strain in Ir shell downshifts the d-band center and weakens the binding of the intermediates, causing the enhanced OER activity. The compressive strain also boosts hydrogen evolution reaction (HER) activity and the strained nanocrystals can be served as excellent catalysts for both anode and cathode in overall water-splitting electrocatalysis.