The cobalt-based metal organic frameworks array derived CoFeNi-layered double hydroxides anode and CoP/FeNi2P heterojunction cathode for ampere-level seawater overall splitting

The seawater electrolysis technology powered by renewable energy is recognized as the promising "green hydrogen" production method to solve serious energy and environmental problems. The lack of low-cost and ampere-level current OER (oxygen evolution reaction) and HER (hydrogen evolution reaction) catalysis limits their industrial application. In this work, a unique tri-metal (Co/Fe/Ni) layered double hydroxide hollow array anode catalyst (CFN-LDH/NF) and the CoP/FeNi2P heterojunction hollow array cathode are successfully prepared via one in-situ growth of Co-MOF on nickel foam (Co-MOF/NF) precursor, which exhibits excellent catalytic performance. The η1000 values of 352 and 392 mV are achieved for CFN-LDH/NF (OER catalyst) in 1.0 M KOH and alkaline seawater solution, respectively. The CFNP/NF with a low overpotential of 281 mV is required to reach 1000 mA cm-2 current density for HER in 1.0 M KOH solution, while the η1000 in alkaline seawater solution is 312 mV. The CFN-LDH/NF||CFNP/NF electrolyzer exhibits excellent long-term durability over 100 h, achieving current density of 500 mA cm-2 at 1.825 V in 1.0 M KOH solution. The construction of hollow tri-metal LDH and phosphides heterostructures may open a new and relatively unexplored path for fabricating high performance seawater splitting catalysis.

Promoting Oxygen Evolution Electrocatalysis by Coordination Engineering in Cobalt Phosphate

Understanding the structure-activity correlation is an important prerequisite for the rational design of high-efficiency electrocatalysts at the atomic level. However, the effect of coordination environment on electrocatalytic oxygen evolution reaction (OER) remains enigmatic. In this work, the regulation of proton transfer involved in water oxidation by coordination engineering based on Co3(PO4)2 and CoHPO4 is reported. The HPO4 2- anion has intermediate pKa value between Co(II)-H2O and Co(III)-H2O to be served as an appealing proton-coupled electron transfer (PCET) induction group. From theoretical calculations, the pH-dependent OER properties, deuterium kinetic isotope effects, operando electrochemical impedance spectroscopy (EIS) and Raman studies, the CoHPO4 catalyst beneficially reduces the energy barrier of proton hopping and modulates the formation energy of high-valent Co species, thereby enhancing OER activity. This work demonstrates a promising strategy that involves tuning the local coordination environment to optimize PCET steps and electrocatalytic activities for electrochemical applications. In addition, the designed system offers a motif to understand the structure-efficiency relationship from those amino-acid residue with proton buffer ability in natural photosynthesis.

Synergistic effect of defects and porous structure in CoCCHH-CoSe heterogeneous-tube @PEDOT:PSS foam towards elastic supercapacitor with enhanced pseudocapacitances

It is still challenging to construct stable 3D energy storage materials at the nanoscale by precise pore structure control and reasonable surface modification. Herein, a novel interwoven porous Co(CO₃)_0.35Cl_0.20(OH)_1.10 (CoCCHH)-CoSe heterogeneous-tube @PEDOT:PSS 3D foam with abundant active sites is presented as supercapacitor electrodes. The electrochemical results indicated that the pore structure provides ample space for redox reaction, and increases the number of ion transport channels. Besides, rational surface modification brings about sufficient active sites for redox reaction. The stable, porous PEDOT:PSS foam with a 3D elastic frame exhibited excellent electrical conductivity. Thus, the CoCCHH-CoSe@PEDOT:PSS foam possessed excellent specific capacitance and energy density, due to the synergistic effect of the unique 3D structure and surface defects. The home-made supercapacitor with CoCCHH-CoSe@PEDOT:PSS foam as cathode materials showed high specific capacitance (440.6F g^-1 at 1 A g^-1) and excellent energy density (137.7 Wh kg^-1). This work provides a valuable strategy to develop potential materials for electrochemical energy storage.

Lowering the onset potential of Zr-doped hematite nanocoral photoanodes by Al co-doping and surface modification with electrodeposited Co-Pi

Herein, in situ zirconium-doped hematite nanocoral (Zr-Fe₂O₃ (I) NC) photoanode was prepared via a specially designed diluted hydrothermal approach and modified with Al³⁺ co-doping and electrodeposited cobalt-phosphate ("Co-Pi") cocatalyst. Firstly, an unintentional in situ Zr-Fe₂O₃ (I)) NC photoanode was synthesized, which achieved an optimum photocurrent density of 0.27 mA/cm² at 1.0 V vs. RHE but possessed a more positively shifted onset potential than conventionally prepared hematite nanorod photoelectrodes. An optimized amount of aluminum co-doping suppresses the bulk as well as surface defects, which causes a negative shift in the onset potential from 0.85 V to 0.8 V vs. RHE and enhances the photocurrent density of Zr-Fe₂O₃(I) NC from 0.27 mA/cm² to 0.7 mA/cm² at 1.0 V vs. RHE. The electrodeposited Co-Pi modification further reduce the onset potential of Al co-doped Zr-Fe₂O₃(I) NC to 0.58 V vs. RHE and yield a maximum photocurrent of 1.1 mA/cm² at 1.0 V vs. RHE (1.8 mA/cm² at 1.23 V vs RHE). The improved photocurrent at low onset potential can be attributed to synergistic effect of Al co-doping and Co-Pi surface modification. Further, during photoelectrochemical water-splitting, a 137 and 67 μmol of hydrogen (H₂) and oxygen (O₂) evolution was achieved over the optimum Co-Pi-modified Al-co-doped Zr-Fe₂O₃(I) NC photoanode within 6 h. The proposed charge transfer mechanism in optimum Co-Pi-modified Alco-doped Zr-Fe₂O₃(I) NC photoanodes during the photoelectrochemical water splitting was also studied.

Fabrication of a Au-loaded CaFe2O4/CoAl LDH p–n junction based architecture with stoichiometric H2 & O2 generation and Cr(vi) reduction under visible light

Visible-light-efficient Au-loaded CaFe₂O₄/CoAl LDH p–n junction for H₂ & O₂ generation and Cr(vi) reduction.

Needle grass-like cobalt hydrogen phosphate on Ni foam as an effective and stable electrocatalyst for the oxygen evolution reaction

Novel three dimensional needle grass-like CoHPO₄·H₂O on Ni foam has been prepared as an effective and robust OER electrocatalyst.

CoHPi Nanoflakes for Enhanced Oxygen Evolution Reaction

Electrochemical splitting of water to produce hydrogen and oxygen is an important process for many energy storage and conversion devices. Developing efficient, robust, low-cost, and earth-abundant electrocatalysts for the oxygen evolution reaction (OER) is therefore of great importance. Herein, we report a novel method to prepare two-dimensional cobalt hydrogen phosphate (CoHPi) through chemical conversion of α-Co(OH)₂ precursor at room temperature. The CoHPi nanoflakes with the thickness of 3 nm contain HPO₄^2- anions, which have been demonstrated to serve as a proton acceptor in proton-coupled electron-transfer (PCET) process of OER. Due to their ultrathin structure and the PCET merit of anions, the CoHPi nanoflakes show enhanced OER activity as well as excellent stability in prolonged OER operation. Through further mechanism study, the observed performances can be ascribed to enriched active sites, surface superhydrophilicity, and rapid electron/proton and mass transfers.

Advanced bi-functional CoPi co-catalyst-decorated g-C3N4 nanosheets coupled with ZnO nanorod arrays as integrated photoanodes

In this work, a CoPi-decorated type II heterojunction composed of one-dimensional (1D) ZnO nanorod arrays (NRAs) coated with two-dimensional (2D) carbon nitride (g-C₃N₄) was successfully prepared and used as photoanode.

Z-Scheme in a Co3(PO4)2/α-Fe2O3 photocatalysis system for overall water splitting under visible light

A Z-scheme Co₃(PO₄)₂/α-Fe₂O₃ structure was designed as an efficient photocatalyst for overall water splitting under visible light.

LaTiO2N-LaCrO3: continuous solid solutions towards enhanced photocatalytic H2 evolution under visible-light irradiation

(LaTiO₂N)_1-x(LaCrO₃)_x continuous solid solutions with an orthorhombic-phase ABX₃ perovskite structure and with varied LaCrO₃ contents (0 ≤ x ≤ 1) were synthesized by a polymerized complex method followed by a post-treatment process of nitridation for the first time. Visible-light-driven photocatalytic H₂-evolution activities of the solid solutions gradually increased with the increase of x from 0.0 to 0.3, and then sharply decreased with the further increase of x from 0.3 to 1.0. With the increase of x, on the one hand, the narrowed bandgaps of solid solutions would enhance the generation of charge carriers and the increased lattice distortion of solid solutions could promote the separation and migration of charge carriers, thus mainly contributing to the improvement of photocatalytic activities; on the other hand, the lowered CBMs of solid solutions would reduce the driving force for reducing H₂O to H₂ and the decreased surface areas of solid solutions would weaken the adsorption of reactants and reduce the reactive sites, thereby resulting in the deterioration of photocatalytic activities.