https://doi.org/10.1016/j.jallcom.2022.166113

Recent advances in non-noble metal-based bifunctional electrocatalysts for overall seawater splitting

Ultrathin Cu2P2O7 nanoflakes on stainless steel substrate for flexible symmetric all-solid-state supercapacitors

This review introduces recent advances of various anion-mixed transition metal compounds (e.g., nitrides, halides, phosphides, chalcogenides, (oxy)hydroxides, and borides) for efficient water electrolysis applications in detail. The challenges and future perspectives are proposed and analyzed for the anion-mixed water dissociation catalysts, including polyanion-mixed and metal-free catalyst, progressive synthesis strategies, advanced in situ characterizations, and atomic level structure-activity relationship. Hydrogen with high energy density and zero carbon emission is widely acknowledged as the most promising candidate toward world's carbon neutrality and future sustainable eco-society. Water-splitting is a constructive technology for unpolluted and high-purity H2 production, and a series of non-precious electrocatalysts have been developed over the past decade. To further improve the catalytic activities, metal doping is always adopted to modulate the 3d-electronic configuration and electron-donating/accepting (e-DA) properties, while for anion doping, the electronegativity variations among different non-metal elements would also bring some potential in the modulations of e-DA and metal valence for tuning the performances. In this review, we summarize the recent developments of the many different anion-mixed transition metal compounds (e.g., nitrides, halides, phosphides, chalcogenides, oxyhydroxides, and borides/borates) for efficient water electrolysis applications. First, we have introduced the general information of water-splitting and the description of anion-mixed electrocatalysts and highlighted their complementary functions of mixed anions. Furthermore, some latest advances of anion-mixed compounds are also categorized for hydrogen and oxygen evolution electrocatalysis. The rationales behind their enhanced electrochemical performances are discussed. Last but not least, the challenges and future perspectives are briefly proposed for the anion-mixed water dissociation catalysts. 

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Shining Light on Anion-Mixed Nanocatalysts for Efficient Water Electrolysis: Fundamentals, Progress, and Perspectives

Single-pot hydrothermal synthesis of manganese phosphate microrods as a cathode material for highly stable flexible solid-state symmetric supercapacitors

In the present study, cobalt manganese phosphate (H-CMP-series) thin films with different compositions of Co/Mn are prepared on stainless steel (SS) substrate via a facile hydrothermal method and employed as binder-free cathode electrodes in a hybrid supercapacitor. The XRD study reveals a monoclinic crystal structure, and the FE-SEM analysis confirmed that H-CMP-series samples displayed a nano/microarchitecture (microflowers to nanoflakes) on the surface of SS substrate with excess available surfaces and unique sizes. Interestingly, the synergy between cobalt and manganese species in the cobalt manganese phosphate thin film electrode demonstrates a maximum specific capacitance of 571 F g-1 at a 2.2 A g-1 current density in 1 M KOH. Besides, the nano/microstructured cobalt manganese phosphate was able to maintain capacitance retention of 88% over 8000 charge-discharge cycles. More importantly, the aqueous/all-solid-state asymmetric supercapacitor manufactured with the cobalt manganese phosphate thin film as the cathode and reduced graphene oxide (rGO) as the anode displays a high operating potential window of 1.6 V. The aqueous asymmetric device exhibited a maximum specific capacitance of 128 F g-1 at a current density of 1 A g-1 with an energy density of 45.7 Wh kg-1 and a power density of 1.65 kW kg-1. In addition, the all-solid-state asymmetric supercapacitor device provides a high specific capacitance of 37 F g-1 at 1 A g-1 with 13.3 Wh kg-1 energy density and 1.64 kW kg-1 power density in a polymer gel (PVA-KOH) electrolyte. The long cyclic life of both devices (87 and 84%, respectively, after 6000 cycles) and practical demonstration of the solid-state device (lighting of a LED lamp) suggest another alternative choice for cathode materials to develop stable energy storage devices with high energy density. Furthermore, the aforementioned study paves the way to investigate phosphate-based materials as a new class of materials for supercapacitor applicability.

Fabrication of a High-Performance Hybrid Supercapacitor Based on Hydrothermally Synthesized Highly Stable Cobalt Manganese Phosphate Thin Films.

Binder-free copper phosphate hydroxide [Cu2(PO4)(OH)] thin films have been prepared on stainless-steel (SS) substrates at 393 K via a facile hydrothermal method. X-ray diffraction analysis confirmed the formation of orthorhombic-structured copper phosphate hydroxide [Cu2(PO4)(OH)] thin films with uniform microstrip-like morphology and Brunauer–Emmett–Teller (BET) surface area of 5.26 m2 g−1. The electrochemical performance of the films depended on their thickness, with a maximum specific capacitance of 280 F g−1 at a scan rate 5 mV s−1 in 1 M KOH electrolyte. The [Cu2(PO4)(OH)] electrode delivered an energy density of 3.85 Wh kg−1 and a power density of 264.70 W kg−1 with excellent (91%) capacitive retention after 2000 cycles. This excellent electrochemical performance shows that such microstrip-like Cu2(PO4)(OH) thin films are promising electrodes for high-performance supercapacitors.

Facile Synthesis of Microstrip-Like Copper Phosphate Hydroxide Thin Films for Supercapacitor Applications

Cobalt doped iron phosphate thin film: An effective catalyst for electrochemical water splitting

Hydrothermally synthesized Iron Phosphate Hydroxide thin film electrocatalyst for electrochemical water splitting

A tunable bandgap without doping is highly desirable for applications in optoelectronic devices. Herein, we develop a new method which can tune the bandgap without any doping. In the present research, the bandgap of Fe2O3 nanostructured films is simply tuned by changing the synthesis temperature. The Fe2O3 nanostructured films are synthesized on ITO/glass substrates at temperatures of 1100, 1150, 1200, and 1250 °C using the hot filament metal oxide vapor deposition (HFMOVD) and thermal oxidation techniques. The Fe2O3 nanostructured films contain two mixtures of Fe2+ and Fe3+ cations and two trigonal (α) and cubic (γ) phases. The increase of the Fe2+ cations and cubic (γ) phase with the elevated synthesis temperatures lifted the valence band edge, indicating a reduction in the bandgap. The linear bandgap reduction of 0.55 eV without any doping makes the Fe2O3 nanostructured films promising materials for applications in bandgap engineering, optoelectronic devices, and energy storage devices.

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Sujit A. Kadam

Papers

Facile Synthesis of Microstrip-Like Copper Phosphate Hydroxide Thin Films for Supercapacitor Applications

Cobalt doped iron phosphate thin film: An effective catalyst for electrochemical water splitting

Hydrothermally synthesized Iron Phosphate Hydroxide thin film electrocatalyst for electrochemical water splitting

Doping-free bandgap tunability in Fe2O3 nanostructured films

Binder free cobalt iron phosphate thin films as efficient electrocatalysts for overall water splitting.