Manageable Bubble Release Through 3D Printed Microcapillary for Highly Efficient Overall Water Splitting

Optimized Bubble Dynamics of 3D-Printed Electrodes for Enhanced Water Splitting

Gas evolution plays an important role in water electrolysis, as sluggish bubble dynamics lead to blockage of active sites, reduced catalytic performance, and even detachment of the catalysts. In this work, we present a strategy to fabricate highly rough three-dimensional (3D)-printed Ni (3DPNi) electrodes with ordered flow channel structures, achieving exceptional catalytic performance through enhanced bubble detachment and transport dynamics. The rough surfaces enhance hydrophilic and aerophobic properties, suppressing bubble coalescence and accelerating bubble detachment dynamics. The ordered structures of 3DPNi serve as efficient bubble flow channels and effectively prevent bubble trapping, facilitating rapid bubble transport dynamics. Collectively, these features optimize bubble dynamics, significantly boosting catalytic performance for water electrolysis. Computational fluid dynamics simulations and visual experiments validate the improved bubble dynamics. When coated with NiFe-LDH (NiFe-LDH/3DPNi), a low overpotential of 238 mV is required to deliver 100 mA cm-2 for OER. In overall water splitting, the NiFe-LDH/3DPNi || Pt plate setup requires a cell voltage of 1.86 V to achieve 1 A cm-2 and demonstrates excellent stability over 100 h at this current density, indicating strong potential for practical applications.

Synergizing superwetting and architected electrodes for high-rate water splitting

Water splitting is one of the most promising technologies for generating green hydrogen. To meet industrial demand, it is essential to boost the operation current density to industrial levels, typically in the hundreds of mA cm-2. However, operating at these high current densities presents significant challenges, with bubble formation being one of the most critical issues. Efficient bubble management is crucial as it directly impacts the performance and stability of the water splitting process. Superwetting electrodes, which can enhance aerophobicity, are particularly favorable for facilitating bubble detachment and transport. By reducing bubble contact time and minimizing the size of detached bubbles, these electrodes help prevent blockage and maintain high catalytic efficiency. In this review, we aim to provide an overview of recent advancements in tackling bubble-related issues through the design and implementation of superwetting electrodes, including surface modification techniques and structural optimizations. We will also share our insights into the principles and mechanisms behind the design of superwetting electrodes, highlighting the key factors that influence their performance. Our review aims to guide future research directions and provides a solid foundation for developing more efficient and durable superwetting electrodes for high-rate water splitting.

Bi-metallic electrochemical deposition on 3D pyrolytic carbon architectures for potential application in hydrogen evolution reaction

3D printing has emerged as a highly efficient process for fabricating electrodes in hydrogen evolution through water splitting, whereas metals are the most popular choice of materials in hydrogen evolution reactions (HER) due to their catalytic activity. However, current 3D printing solutions face challenges, including high cost, low surface area, and sub-optimal performance. In this work, we introduce metal-deposited 3D printed pyrolytic carbon (PyC) as a facile and cost-effective HER electrode. We adopt an integrated approach of resin 3D printing, pyrolysis, and electrochemical metal deposition. 3D printing of a resin and its subsequent pyrolysis led to 3D complex architectures of the conductive substrate, facilitating the electrochemical metal deposition and leading to layered 3D metal architecture. Both monolayers of metals (such as copper and nickel) and bi-metallic 3D PyC structures are demonstrated. Each metal layer thickness ranges from 6 to10 µm. The metal coatings, particularly the bi-metallic configurations, result in achieving significantly higher mechanical properties under compressive loading and improved electrical properties due to the synergistic contributions from each metal counterpart. The metalized PyC structures are further demonstrated for HER catalysts, contributing to the development of highly efficient and durable catalyst systems for hydrogen production. Among the materials studied here, Ni@Cu bimetallic 3D PyC electrodes are particularly well-suited, demonstrating a low HER overpotential value of 264 mV (100 mA/cm2, KOH (1 M)) with corresponding Tafel slopes of 107 mV/dec, with exceptional stability during a 10 h operation at a high applied current of -50 mA/cm2.

Capillary-Driven Separate Gas-Liquid Transport: Alleviating Mass Transport Losses for Efficient Hydrogen Evolution

Developing earth-abundant transition metal electrodes with high activity and durability is crucial for efficient and cost-effective hydrogen production. However, numerous studies in the hydrogen evolution reaction (HER) primarily focus on improving the inherent activity of catalysts, and the critical influence of gas-liquid countercurrent transport behavior is often overlooked. In this study, we introduce the concept of separate-path gas-liquid transport to alleviate mass transport losses for the HER by developing a novel hierarchical porous Ni-doped cobalt phosphide electrode (CoNix-P@Ni). The CoNix-P@Ni electrodes with abundant microvalleys and crack structures facilitate the gas-liquid cotransport by separating the bubble release and water supply paths. Visualization and numerical simulation results demonstrate that cracks primarily serve as water supply paths, with capillary pressure facilitating the transport of water from the cracks to the microvalleys. This process ensures the continuous wetting of electrolytes in the electrode, reduces hydrogen supersaturation near the active site, and increases hydrogen transport flux to the microvalleys for accelerating bubble growth. Additionally, the microvalleys act as preferential sites for bubble evolution, preventing bubble coverage on other active sites. By regulating the amount of nickel, the CoNi1-P@Ni electrode exhibited the smallest and densest microvalleys and cracks, achieving superior HER performance with an overpotential of 51 mV at 10 mA cm-2. The results offer a promising direction for constructing high-performance HER electrodes.

3D printed energy devices: generation, conversion, and storage

The energy devices for generation, conversion, and storage of electricity are widely used across diverse aspects of human life and various industry. Three-dimensional (3D) printing has emerged as a promising technology for the fabrication of energy devices due to its unique capability of manufacturing complex shapes across different length scales. 3D-printed energy devices can have intricate 3D structures for significant performance enhancement, which are otherwise impossible to achieve through conventional manufacturing methods. Furthermore, recent progress has witnessed that 3D-printed energy devices with micro-lattice structures surpass their bulk counterparts in terms of mechanical properties as well as electrical performances. While existing literature focuses mostly on specific aspects of individual printed energy devices, a brief overview collectively covering the wide landscape of energy applications is lacking. This review provides a concise summary of recent advancements of 3D-printed energy devices. We classify these devices into three functional categories; generation, conversion, and storage of energy, offering insight on the recent progress within each category. Furthermore, current challenges and future prospects associated with 3D-printed energy devices are discussed, emphasizing their potential to advance sustainable energy solutions.

Robust and Corrosion-Resistant Overall Water Splitting Electrode Enabled by Additive Manufacturing

Electrolysis of water has emerged as a prominent area of research in recent years. As a promising catalyst support, copper foam is widely investigated for electrolytic water, yet the insufficient mechanical strength and corrosion resistance render it less suitable for harsh working conditions. To exploit high-performance catalyst supports, various metal supports are comprehensively evaluated, and Ti6Al4V (Ti64) support exhibited outstanding compression and corrosion resistance. With this in mind, a 3D porous Ti64 catalyst support is fabricated using the selective laser sintering (SLM) 3D printing technology, and a conductive layer of nickel (Ni) is coated to increase the electrical conductivity and facilitate the deposition of catalysts. Subsequently, Co0.8Ni0.2(CO3)0.5(OH)·0.11H2O (CoNiCH) nanoneedles are deposited. The resulting porous Ti64/Ni/CoNiCH electrode displayed an impressive performance in the oxygen evolution reaction (OER) and reached 30 mA cm-2 at an overpotential of only 200 mV. Remarkably, even after being compressed at 15.04 MPa, no obvious structural deformation is observed, and the attenuation of its catalytic efficiency is negligible. Based on the computational analysis, the CoNiCH catalyst demonstrated superior catalytic activity at the Ni site in comparison to the Co site. Furthermore, the electrode reached 30 mA cm-2 at 1.75 V in full water splitting conditions and showed no significant performance degradation even after 60 h of continuous operation. This study presents an innovative approach to robust and corrosion-resistant catalyst design.

Hierarchical CoWO4/NixFeyS microspheres bearing crystalline-amorphous interface as a multifunctional platform for outperformed water splitting and sensitive hydrazine sensing

Highly efficient and multifunctional electrocatalysts are of high value in energy transformation and electrochemical sensing. Herein, hierarchically architectured cobalt tungstate/nickel iron sulfide (CoWO4/NixFeyS) microspheres with a crystalline-amorphous interface have been prepared on bimetallic substrate of nickel-iron foam (NIF) by a two-step hydrothermal method. Electrochemical characterization shows that CoWO4/NixFeyS microspheres can boost the electrocatalytic activity effectively through the synergistic effect on the crystalline-amorphous interface. When the CoWO4/NixFeyS is applied as the electrocatalysts for oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER), the overpotentials at a high current density of 500 mA cm-2 are only 322.8 mV and 306.5 mV, respectively. The overall water splitting device composed of CoWO4/NixFeyS/NIF couple only needs a cell voltage of 1.80 V to reach a current density of 100 mA cm-2, and 2.19 V to reach 500 mA cm-2. The CoWO4/NixFeyS/NIF can be also utilized as an effective electrochemical platform for the sensing of toxic hydrazine in a wide range from 50 μM to 17.3 mM, with a detection limit of 46.4 μM. All these results display that the CoWO4/NixFeyS/NIF can be a high-performance multifunctional material for energy transformation and environmental pollutant monitoring.

Bubble Management for Electrolytic Water Splitting by Surface Engineering: A Review

During electrocatalytic water splitting, the management of bubbles possesses great importance to reduce the overpotential and improve the stability of the electrode. Bubble evolution is accomplished by nucleation, growth, and detachment. The expanding nucleation sites, decreasing bubble size, and timely detachment of bubbles from the electrode surface are key factors in bubble management. Recently, the surface engineering of electrodes has emerged as a promising strategy for bubble management in practical water splitting due to its reliability and efficiency. In this review, we start with a discussion of the bubble behavior on the electrodes during water splitting. Then we summarize recent progress in the management of bubbles from the perspective of surface physical (electrocatalytic surface morphology) and surface chemical (surface composition) considerations, focusing on the surface texture design, three-dimensional construction, wettability coating technology, and functional group modification. Finally, we present the principles of bubble management, followed by an insightful perspective and critical challenges for further development.