Effect of Copper Cobalt Oxide Composition on Oxygen Evolution Electrocatalysts for Anion Exchange Membrane Water Electrolysis

Effect of applied potential on the optical and electrical properties of Cu2CoO3

The effect of the applied potential on the crystallography, morphology, optical, and electrical properties of copper-cobalt oxide (Cu2CoO3) co-electrodeposited on ITO (Indium Tin Oxide) substrate has been studied. The electrochemical behavior of Cu2CoO3 using cyclic voltammetry showed that the co-electrodeposition of Cu2CoO3 occurred at a negative potential of - 0.70 V versus SCE, following a quasi-reversible reaction controlled by the diffusion process. Chronoamperometry (CA) revealed that the nucleation and growth mechanism of Cu2CoO3 follows the instantaneous three-dimensional process according to Scharifker and Hill model. X-ray diffraction (XRD) analysis indicated that the resulting layers at different applied potentials exhibited an orthorhombic structure with a preferred orientation of the crystallites (011) plan. The morphology of the surface changes with potential applied. Furthermore, the optical properties of the copper and cobalt oxide films were investigated using UV-visible spectroscopy; showing that the band gap energy for all the materials increases when the applied potential decreases. The Cu2CoO3 layers obtained are p-type semiconductors. The acceptor density (NA) increases with decreasing applied potential.

Fluorine-Containing Poly(Fluorene)-Based Anion Exchange Membrane with High Hydroxide Conductivity and Physicochemical Stability for Water Electrolysis

Improving the hydroxide conductivity and dimensional stability of anion exchange membranes (AEMs) while retaining their high alkaline stability is necessary to realize the commercialization of AEM water electrolysis (AEMWE). A strategy for improving the hydroxide conductivity and dimensional stability of AEMs by inserting fluorine atoms in the core structure of the backbone is reported, which not only reduces the glass transition temperature of the polymer due to steric strain, but also induces distinct phase separation by inducing polarity discrimination to facilitate the formation of ion transport channels. The resulting PFPFTP-QA AEM with fluorine into the core structure shows high hydroxide conductivity (>159 mS cm-1 at 80 °C), favorable dimensional stability (>25% at 80 °C), and excellent alkaline stability for 1000 h in 2 m KOH solution at 80 °C. Moreover, the PFPFTP-QA is used to construct an AEMWE cell with a platinum group metal (PGM)-free NiFe anode, which exhibits the current density of 6.86 A cm-2 at 1.9 V at 80 °C, the highest performance in Pt/C cathode and PGM-free anode reports so far and operates stably for over 100 h at a constant current of 0.5 A cm-2.

Mn-doped Sequentially Electrodeposited Co-based Oxygen Evolution Catalyst for Efficient Anion Exchange Membrane Water Electrolysis

Designing high-performance and durable oxygen evolution reaction (OER) catalysts is important for green hydrogen production through anion exchange membrane water electrolysis (AEMWE). Herein, a series of Mn-doped Co-based OER catalysts supported on FeOxHy (FCMx) are presented to enhance the OER activity. Mn doping effectively reduces the size of the Co oxide particles, thereby augmenting the active surface area. Moreover, Mn doping induces the creation of oxygen vacancies, leading to an efficient structural conversion during the OER, which is confirmed via in situ Raman spectroscopy. Under optimal conditions, the catalyst exhibits an overpotential of 234.4 mV at 10 mA cm-2 and a Tafel slope of 37.2 mV dec-1 under half-cell conditions. The AEMWE single-cell system demonstrates a current density of 1560 mA cm-2 at 1.8 V at 60 °C with a degradation rate of 0.4 mV h-1 for 500 h at 500 mA cm-2. Our development of a robust OER catalyst represents notable progress in the field of nonprecious-metal water electrolysis, marking a step toward cost-effective green hydrogen production.

A Polymer-Derived Co(Fe)Ox Oxygen Evolution Catalyst Benefiting from the Oxidative Dehydrogenative Coupling of Cobalt Porphyrins

Thin films of cobalt porphyrin conjugated polymers bearing different substituents are prepared by oxidative chemical vapor deposition (oCVD) and investigated as heterogeneous electrocatalysts for the oxygen evolution reaction (OER). Interestingly, the electrocatalytic activity originates from polymer-derived, highly transparent Co(Fe)Ox species formed under operational alkaline conditions. Structural, compositional, electrical, and electrochemical characterizations reveal that the newly formed active catalyst greatly benefited from both the polymeric conformation of the porphyrin-based thin film and the inclusion of the iron-based species originating from the oCVD reaction. High-resolution mass spectrometry analyses combined with density functional theory (DFT) calculations showed that a close relationship exists between the porphyrin substituent, the extension of the π-conjugated system cobalt porphyrin conjugated polymer, and the dynamics of the polymer conversion leading to catalytically active Co(Fe)Ox species. This work evidences the precatalytic role of cobalt porphyrin conjugated polymers and uncovers the benefit of extended π-conjugation of the molecular matrix and iron inclusion on the formation and performance of the true active catalyst.

Perovskite-based electrocatalysts for oxygen evolution reaction in alkaline media: A mini review

Water electrolysis is one of the attractive technologies for producing clean and sustainable hydrogen fuels with high purity. Among the various kinds of water electrolysis systems, anion exchange membrane water electrolysis has received much attention by combining the advantages of alkaline water electrolysis and proton exchange membrane water electrolysis. However, the sluggish kinetics of the oxygen evolution reaction, which is based on multiple and complex reaction mechanisms, is regarded as a major obstacle for the development of high-efficiency water electrolysis. Therefore, the development of high-performance oxygen evolution reaction electrocatalysts is a prerequisite for the commercialization and wide application of water electrolysis systems. This mini review highlights the current progress of representative oxygen evolution reaction electrocatalysts that are based on a perovskite structure in alkaline media. We first summarize the research status of various kinds of perovskite-based oxygen evolution reaction electrocatalysts, reaction mechanisms and activity descriptors. Finally, the challenges facing the development of perovskite-based oxygen evolution reaction electrocatalysts and a perspective on their future are discussed.

Multistep Sulfur Leaching for the Development of a Highly Efficient and Stable NiSx/Ni(OH)2/NiOOH Electrocatalyst for Anion Exchange Membrane Water Electrolysis

Nickel (poly)sulfides have been widely studied as anodic catalysts for alkaline water electrolysis owing to their diverse morphologies, high catalytic activities in the oxygen evolution reaction (OER), and low cost. To utilize low-cost and high-efficiency polysulfides with industry-relevant cycling stability, we develop a Ni-rich NiS_x/Ni(OH)₂/NiOOH catalyst derived from NiS₂/Ni₃S₄ nanocubes. Ni-rich NiS_x/Ni(OH)₂/NiOOH shows improved OER catalytic activity (η = 374 mV@50 mA cm^-2) and stability (0.1% voltage increase) after 65 h of a galvanostatic test at 10 mA cm^-2 compared with commercial Ni/NiO and hydrothermally synthesized Ni(OH)₂ (both show η > 460 mV@50 mA cm^-2 along with 4.40 and 1.92% voltage increase, respectively). A water-splitting electrolyzer based on Pt/C||AF1-HNN8-50||NiS_x/Ni(OH)₂/NiOOH exhibits a current density of 1800 mA cm^-2 at 2.0 V and 500 h high-rate stability at 1000 mA cm^-2 with negligible attenuation of only 0.12 mV h^-1. This work provides an understanding of truly stable species, intrinsic active phases of Ni polysulfides, their high-rate stability in a real cell, and sheds light on the development of stable chalcogenide-based anodic electrocatalysts for anion exchange membrane water electrolysis (AEMWE).