Bubble size distribution and electrode coverage at porous nickel electrodes in a novel 3-electrode flow-through cell

A novel 3-electrode cell type is introduced to run parametrical studies of H₂ evolution in an alkaline electrolyte on porous electrodes. Electrochemical methods combined with a high-speed optical measurement system are applied simultaneously to characterize the electrodes and the bubble dynamics in terms of bubble size distribution and coverage of the working electrode. Three different cathodes made of expanded nickel are investigated at applied current densities of |j| = 10–200 mA cm^?2 without forced flow and at a flow rate of 5 ml min^?1. The applied current density is found to significantly influence both the size of detached bubbles and the surface coverage of the working electrode. The forced flow through the cathodes is found to strongly reduce the bubble size up to current densities of about 100 mA cm^?2, whereas the initial transient until the cathode surface is completely covered by bubbles is only marginally affected by the flow-through.     

Introduction of a new active and stable cathode catalyst based on bimetal-organic frameworks/PPy-sheet for alkaline direct ethanol fuel cell

For the first time, the polypyrrole (PPy) with a sheet-like structure was synthesized by a high-efficiency and facile chemical reaction process. A new composite with the growth of bimetallic zeolitic imidazolate frameworks on polypyrrole sheet-like (BMZIF@PPy) was synthesized. Then, the BMZIF@PPy composite by different heat-treatment temperatures is applied to make oxygen reduction reaction (ORR) electrocatalysts. Electrochemical measurements perform to investigate the ORR properties in both acidic and alkaline media. The onset potential and the limiting current density for the Cobalt/Zinc-nanocarbon@polypyrrole pyrolysis at 800 °C (Co/Zn-NC@PPy-800) were 0.977 V_RHE and 4.99 mA cm^?2 in 0.1 M KOH and 0.85V_RHE and 5.48 mA cm^?2 in 0.5 M H₂SO₄. Finally, due to the good activity and stability in alkaline media, the Co/Zn-NC@PPy-800 electrocatalyst is used as the cathode in an alkaline direct ethanol fuel cell. The maximum power of the Co/Zn-NC@PPy-800 cathode catalyst was 77% higher than that of the commercial Pt/C electrocatalyst.     

Fabrication and evaluation of passive alkaline membraneless microfluidic DMFC

The fabrication and evaluation of a passive, air-breathing, membraneless microfluidic direct methanol fuel cell (ML-μDMFC) using a methanol-tolerant Ag/Pt/CP cathode is presented here. We previously proposed that due to its high tolerance to methanol and the good activity towards the oxygen reduction reaction in alkaline medium, this catalyst could be useful to reduce the methanol crossover effect in direct methanol fuel cells. Therefore, in order to demonstrate it, we designed and fabricated a microfluidic device that allowed the evaluation of the cathode in a high fuel concentration environment, using up to 5 M MeOH in 0.5 M KOH in passive mode. The results confirmed the high tolerance to MeOH and the ORR selectivity of the Ag/Pt/CP cathode, in contrast with a Pt/CP cathode, where performance decreased severely due to the methanol crossover. Employing the methanol-tolerant cathode, it was possible to obtain a power density of 2.4 mW cm⁻². Additionally, the durability studies revealed more stability for the ML-μDMFC using the bimetallic catalyst, compared with Pt/CP.     

Construction of WS2 triangular nanoplates array for hydrogen evolution reaction over a wide pH range

As a classic transition metal dichalcogenide, WS₂ has been synthesized by a variety of methods towards different applications. However, few of them are vertically grown self-templated structures, besides, all the reported WS₂ for hydrogen evolution reaction (HER) are in acidic media. Herein, we use a simple method to synthesize a new morphological WS₂ triangular nanoplates array through the sulfuration of hydrothermally obtained WO₃ nanowires on carbon cloth (WS₂TN/CC). The WS₂TNs are equilateral triangle with large surface area that grown vertically on carbon fiber. The WS₂TN/CC exhibits good catalytic activity and stability as electrocatalyst for HER in acidic media and firstly in both neutral and alkaline media. The overpotential of 196, 150 and 193 mV are needed to afford current density of 10 mA cm⁻² in acidic, neutral and alkaline media, respectively.     

Bimetallic metal-organic framework derived electrocatalyst for efficient overall water splitting

The development of bifunctional catalysts that can be applied to both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is widely regarded as a key factor in the production of sustainable hydrogen fuel by electrochemical water splitting. In this work, we present a high-performance electrocatalyst based on nickel-cobalt metal-organic frameworks for overall water splitting. The as-obtained catalyst shows low overpotential to reaches the current density of 10 mA cm⁻² with 249 mV for OER and 143 mV for HER in alkaline media, respectively. More importantly, when the electrolyzer was assembled with the as-prepared catalyst as anode and cathode simultaneously, it demonstrates excellent activity just applies a potential of 1.68 V to achieve 10 mA cm⁻² current density for overall water splitting.     

Hydrothermally/electrochemically decorated FeSe on Ni-foam electrode: An efficient bifunctional electrocatalysts for overall water splitting in an alkaline medium

A new hybrid catalyst based on Ni foam (NF) and FeSe was prepared by a facial hydrothermal method, in which Se-decorated NF was subsequently electrochemically doped by Fe. Binder-free catalyst containing electrodes were directly tested for the hydrogen and oxygen evolution reaction (HER/OER). The FeSe/NF electrode displayed an OER current density of 100 mA cm⁻² at potential of 1.42 V, and a relatively small Tafel slope of 109 mV dec⁻¹ in a 1 M KOH solution. Also, FeSe/NF electrode exhibited reasonable HER overpotential of 200 mV at 10 mAcm⁻² current density with Tafel slope of 145 mV dec⁻¹. The XRD and TEM studies revealed that the formation of heterogeneous interfaces of NiSe₂ and FeSe₂,generated more active sites that can promote better ions and electron transport in the electrode/electrolyte interfaces. Furthermore, HRTEM analysis indicates that FeSe₂ rich in Se vacancy defects can be created with suitable M − O and M − H bond for better OER and HER performance, respectively. In a-two electrode alkaline water electrolyzer, current densities of 10 mA cm⁻² and 50 mA cm⁻² were obtained at cell voltages of 1.52 V and 1.85 V, respectively, using pure FeSe–NF as both the cathode and anode.     

In-situ growth of Fe–Co Prussian-blue-analog nanocages on Ni(OH)2/NF and the derivative electrocatalysts with hierarchical cage-on-sheet architectures for efficient water splitting

To design an efficient and cost-effective electrocatalyst based on Prussian blue and its analogs are a promising choice to realize energy transformation and storage via water-splitting. Herein, a facile and practical method is developed to in-situ grow Fe–Co Prussian-blue-analog (PBA) nanocages with an open hole in each face center on Ni(OH)₂/NF substrate to form the hierarchical cage-on-plate structure. Furthermore, the Fe–Co PBA nanocages attached to Ni(OH)₂/NF plates are hydrogenated and nitrogenized into FeCoNi/NF and FeCoNiN/NF electrodes, respectively. As-prepared electrodes successfully retain the 3D hierarchical micro-nano structures of Fe–Co PBA@Ni(OH)₂/NF precursor and can be used as a bifunctional water-splitting catalyst for overall water splitting. Compared to FeCoNi/NF, FeCoNiN/NF shows more efficiency and durability in the electrolytic water splitting tests in alkaline media. For the FeCoNiN/NF electrocatalyst, ultralow overpotentials for hydrogen evolution reaction (HER) are only 56 and 290 mV at current densities of 10 and 500 mA cm^?2. Meanwhile, overpotentials for oxygen evolution reaction (OER) are 267 and 374 mV at current densities of 50 and 500 mA cm^?2. The FeCoNiN/NF electrode can act both the cathode and the anode for overall water splitting, this electrolyzer only requires a cell voltage of 1.492 V to afford a current density of 10 mA cm^?2. This electrolyzer can stably deliver a viable high current density of 625 mA cm^?2 for 40 h to meet the condition of industrial application.     

A highly active composite electrocatalyst Ni–Fe–P–Nb2O5/NF for overall water splitting

This work demonstrates a facile Nb₂O₅-decorated electrocatalyst to prepare cost-effective Ni–Fe–P–Nb₂O₅/NF and compared HER & OER performance in alkaline media. The prepared electrocatalyst presented an outstanding electrocatalytic performance towards hydrogen evolution reaction, which required a quite low overpotential of 39.05 mV at the current density of ?10 mA cm^?2 in 1 M KOH electrolyte. Moreover, the Ni–Fe–P–Nb₂O₅/NF catalyst also has excellent oxygen evolution efficiency, which needs only 322 mV to reach the current density of 50 mA cm^?2. Furthermore, its electrocatalytic performance towards overall water splitting worked as both cathode and anode achieved a quite low potential of 1.56 V (10 mA cm^?2).     

A direct formate microfluidic fuel cell with cotton thread-based electrodes

A direct formate microfluidic fuel cell with cotton thread-based electrodes is proposed. The palladium catalyst is directly coated on cotton threads by repeated dipping method to prepare electrodes, which integrates the flow channel and electrode together and provides exposed active sites for enhancing the mass transfer on the anode and cathode. The aqueous anolyte and catholyte transport through cotton threads by capillary force with aid of gravity, eliminating the use of any external pump and facilitating the integration and miniaturization of the whole system. In the experiment, a three-flow channel structure is employed. The fuel is sodium formate and the oxidant is hydrogen peroxide. 1 M Na₂SO₄ solution is introduced into the middle channel formed by cotton threads with no catalyst to alleviate the reactant crossover. Performance is evaluated under various catalyst loadings, fuel concentrations and differences in height between the inlet and outlet. Results show that the fuel cell produces an open circuit voltage (OCV) of 1.41 V. The maximum current density of 74.56 mA cm⁻² and the peak power density of 24.75 mW cm⁻² are yielded when the palladium loading is 1 mg cm⁻¹ and the difference in height between the inlet and outlet is 7 cm, using 4 M HCOONa as fuel. Furthermore, the performance of the fuel cell increases first and then decreases with increasing the palladium loading. The same variation is observed with increasing the fuel concentration. However, the performance gradually increases with increasing the difference in height from 3 cm to 7 cm. The proposed microfluidic fuel cell with cotton thread-based electrodes shows enormous potential as a micro power source for portable devices.     

Iron phthalocyanine as a cathode catalyst for a direct borohydride fuel cell

A direct borohydride fuel cell (DBFC) is constructed using a cathode based on iron phthalocyanine (FePc) catalyst supported on active carbon (AC), and a AB₅-type hydrogen storage alloy (MmNi_3.55Co_0.75Mn_0.4Al_0.3) was used as the anode catalyst. The electrochemical properties are investigated by cyclic voltammetry (CV), linear sweep voltammetry (LSV), etc. methods. The electrochemical experiments show that FePc-catalyzed cathode not only exhibits considerable electrocatalytic activity for oxygen reduction in the BH₄⁻ solutions, but also the existence of BH₄⁻ ions has almost no negative influences on the discharge performances of the air-breathing cathode. At the optimum conditions of 6 M KOH + 0.8 M KBH₄ and room temperature, the maximal power density of 92 mW cm⁻² is obtained for this cell with a discharge current density of 175 mA cm⁻² at a cell voltage of 0.53 V. The new type alkaline fuel cell overcomes the problem of the conventional fuel cell in which both noble metal catalysts and expensive ion exchange membrane were used.     

Vanadium doped cobalt phosphide nanorods array as a bifunctional electrode catalyst for efficient and stable overall water splitting

For the sake of sustainable development, water splitting without other pollutants has been a candidate technology in green energy. Due to the low efficiency of water splitting, innovative breakthroughs are desirable to improve efficiency significantly. Nowadays, the rational design of non-precious metal-based robust bifunctional catalysts is considered to be a feasible way to promote both the cathodic hydrogen evolution reaction (HER) and anodic oxygen evolution reaction (OER). Herein, we proposed a vanadium doped CoP nanorods array catalyst grown on carbon cloth (V–CoP NRs/CC) as a bifunctional electrode material. When V–CoP NRs/CC employed as both anode and cathode materials, it only demands low cell voltages of 1.491 V and 1.606 V to drive a current density of 10 mA cm^?2 (j₁₀) and 50 mA cm^?2 (j₅₀) in 1 M KOH alkaline electrolyte. Especially, V–CoP NRs/CC can maintain its outstanding electrocatalytic performance for more than 40 h at j₅₀ in overall water splitting.     

Air-breathing membraneless laminar flow-based fuel cell with flow-through anode

This paper describes a detailed characterization of laminar flow-based fuel cell (LFFC) with air-breathing cathode for performance (fuel utilization and power density). The effect of flow-over and flow-through anode architectures, as well as operating conditions such as different fuel flow rates and concentrations on the performance of LFFCs was investigated. Formic acid with concentrations of 0.5 M and 1 M in a 0.5 M sulfuric acid solution as supporting electrolyte were exploited with varying flow rates of 20, 50, 100 and 200 μl/min. Because of the improved mass transport to catalytic active sites, the flow-through anode showed improved maximum power density and fuel utilization per single pass compared to flow-over planar anode. Running on 200 μl/min of 1 M formic acid, maximum power densities of 26.5 mW/cm² and 19.4 mW/cm² were obtained for the cells with flow-through and flow-over anodes, respectively. In addition, chronoamperometry experiment at flow rate of 100 μl/min with fuel concentrations of 0.5 M and 1 M revealed average current densities of 34.2 mA/cm² and 52.3 mA/cm² with average fuel utilization of 16.3% and 21.4% respectively for flow-through design. The flow-over design had the corresponding values of 25.1 mA/cm² and 35.5 mA/cm² with fuel utilization of 11.1% and 15.7% for the same fuel concentrations and flow rate.     

Innovative water management in micro air-breathing polymer electrolyte membrane fuel cells

The role of cathodic cover opening ratio on water management was investigated for micro air-breathing polymer electrolyte membrane fuel cells (PEMFCs). The results demonstrate the possibility to manage water content in micro-PEMFC using cover opening ratio variation. By measuring the internal resistance of a cell in various cover configurations (0.33 Ω cm² to 4.0 Ω cm²), the influence of cover opening ratio on water management was shown. Indeed, for a cell situated in a 10% relative humidity atmosphere and operated at 0.5 V, the addition of a 5% opening ratio cover allowed to reach similar current densities (270 mA cm⁻²) to those recorded for the same potential at 70% relative humidity without cover. Although the starting current density for a cell operated at 60 °C without gas humidification was extremely low (15 mA cm⁻²), the total closure of the cover allowed to maintain the water produced and accumulated by the cell at the cathode, and current density of 800 mA cm⁻² were reached after height minutes of operation. The influence of the opening ratio on back-diffused water was also evaluated and the maximum of back-diffused water was observed for a cell operated with a 5% cover opening ratio and represented 33% of the total water product at 150 mA cm⁻².A new method of anodic water evacuation, which does not increase the cell volume and which does not require any control tool was carried out and experimentally evaluated.     

A solid oxide carbon fuel cell operating on pomelo peel char with high power output

The pomelo peel char (PC) was prepared and used as fuel for solid oxide electrolyte direct carbon fuel cells with nickel‐yttrium stabilized zirconia anode, thin‐film YSZ electrolyte, and La_0.8Sr_0.2MnO₃ cathode. The power densities of fuel cells operating on PC and catalyst‐loaded PC (PCC) fuels achieved 309 and 518 mW cm^?2 at 850°C, respectively, which are among the highest power densities reported in the literature on DCFCs. The PC exhibited superior gasification reactivity than coal char due to its unique reticulated foam carbon structure with a homogeneously distributed inherent catalyst. The stability tests at a current density of 50 mA cm^?2 and 825°C indicate that the cell using PC fuel operated in a more stable manner than that using PCC, and the fuel availabilities for PC and PCC were 47.25% and 34.71%, respectively. The results suggest that PC is a promising solid carbonaceous fuel for solid oxide electrolyte direct carbon fuel cells based on its adequate gasification reactivity and high compatibility with the fuel cells.     

Quick-to-synthesize hybrid electrodes composed of activated carbon cloth with Co/Fe-based films as bifunctional electrocatalysts for water splitting

Hybrid electrodes have recently been investigated as attractive alternatives to noble-metal-based electrocatalysts for hydrogen production by water splitting. Herein, we propose an electrode composed of an oxidized carbon cloth with an electrodeposited bimetallic Co/Fe-based film. By optimizing the electrodeposition conditions and applying electrochemically activated carbon cloth as a substrate, one can prepare a free-standing noble-metal-free electrocatalytic electrode with high bifunctional electrocatalytic activity in hydrogen and oxygen evolution from alkaline solution. The developed Fe_0.25Co_0.75 electrode requires overpotentials of 245 mV for HER and 360 mV for OER at high current densities of −100 and 100 mA cm⁻², respectively. Furthermore, its overall synthesis time from commercially available raw materials is only approximately 20 min. The electrode material was used as both a cathode and an anode in the model electrolyzer, which can deliver 10 mA cm⁻² of current density at 1.66 V without loss of activity during 100 h of performance.     

Investigation of the effect of cathode stoichiometry of proton exchange membrane fuel cell using localized electrochemical impedance spectroscopy based on print circuit board

Proton Exchange Membrane Fuel Cell can have a large active area, and the working condition in different areas can be entirely different. Localized electrochemical impedance spectroscopy can directly observe the proton exchange membrane fuel cell internal reaction conditions. In this work, localized electrochemical impedance spectroscopy test system based on print circuit board is implemented in a 50 cm² multi-channel serpentine flow fields. The localized electrochemical impedance spectroscopy performances of different segments with different cathode stoichiometry (1.8, 2.3 and 2.8) at different current density (100  mA cm⁻², 500  mA cm⁻² and 900 mA cm⁻²) are studied. The result demonstrates that the fuel cell may suffer from local drying and flooding at the same time. To make full use of the potential of a fuel cell, a suitable cathode stoichiometry should be identified to control the drying of the inlet and the flooding of the outlet at the same time. It is shown that a cathode stoichiometry of 2.3 is close to the optimum cathode stoichiometry to keep the fuel cell in good consistency without gas waste. Besides, a current density distribution measurement is performed to verify the conclusions of this work.     

Response to Disselkamp: Direct peroxide/peroxide fuel cell as a novel type fuel cell

Besides hydrogen peroxide is known as conventionally oxidizer, it is both a fuel and a source of ignition. Platinum is not suitable catalyst for oxidation and reduction of hydrogen peroxide, because it directly converts the hydrogen peroxide to oxygen gas. In this study, the oxidation mechanism of peroxide is investigated and a fuel cell operating with acidic peroxide as oxidant and basic peroxide as fuel is constructed. The peroxide oxidation reaction in novel alkaline direct peroxide/peroxide fuel cell (DPPFC), shown feasible here using less expensive carbon supported Nickel catalyst, makes the alkaline direct peroxide/peroxide fuel cell a potentially low cost technology compared to PEM fuel cell technology, which employs platinum catalysts. The power density of 3.75 mW cm⁻² at a cell voltage of 0.55 V and a current density of 14 mA cm⁻² was achieved in our fuel cell.     

Development of an air-breathing direct methanol fuel cell with the cathode shutter current collectors

An air-breathing direct methanol fuel cell with a novel cathode shutter current collector is fabricated to develop the power sources for consumer electronic devices. Compared with the conventional circular cathode current collector, the shutter one improves the oxygen consumption and mass transport. The anode and cathode current collectors are made of stainless steel using thermal stamping die process. Moreover, an encapsulation method using the tailor-made clamps is designed to assemble the current collectors and MEA for distributing the stress of the edges and inside uniformly. It is observed that the maximum power density of the air-breathing DMFC operating with 1 M methanol solution achieves 19.7 mW/cm² at room temperature. Based on the individual DMFCs, the air-breathing stack consisting of 36 DMFC units is achieved and applied to power a notebook computer.     

Experimental and numerical investigation on effects of cathode flow field configurations in an air-breathing high-temperature PEMFC

Air-breathing high-temperature proton exchange membrane fuel cell (HT-PEMFC) gets rid of the cumbersome air supplying systems and avoids the water flooding problem by directly exposing the cathode to air and operating the fuel cell at elevated temperature. Performance of the air-breathing HT-PEMFC is dependent on many factors particularly the cathode flow field configurations. However, studies about air-breathing HT-PEMFCs are quite limited in the literature. In the present study, an experimental testing system was setup for the performance measurement of the air-breathing HT-PEMFC. A 3D numerical model was established and validated by the experimental data. Effects of the cathode flow field configurations including the opening shape, end plate thickness, open ratio and opening direction on performance of the air-breathing HT-PEMFC were experimentally and numerically investigated. It was found that the cathode end plate thickness and upward or sideways orientation have the least effect on the performance. The maximum power density of 160 mW/cm² at the current density of 394 mA/cm² can be achieved for the cathode flow field with slot holes and an open ratio of 75%.     

Ionothermal synthesis of N-doped carbon supported CoMn2O4 nanoparticles as ORR catalyst in direct glucose alkaline fuel cell

In this paper, CoMn₂O₄/NC nanocomposites were synthesized via a facile ionothermal synthesis route, and their electrocatalytic performance for oxygen reduction reaction (ORR) was investigated in a direct glucose alkaline fuel cell (DGAFC). The CoMn₂O₄ spinel supported on nitrogen-doped carbon was successfully synthesized with the assistance of the ionic liquid [C₆mim]Cl. The nanocomposite exhibited excellent electrocatalytic activity towards ORR. Especially, CoMn₂O₄/NC achieved a half wave potential of 0.81 V (vs RHE) and a maximum diffusion limiting current density of 5.2 mA cm^?2, that are very close to commercial Pt/C catalyst (E_1/2 = 0.83 V vs RHE, J_d = 5.0 mA cm^?2). In addition, the catalytic performance of CoMn₂O₄/NC was investigated in DGFC. The fuel cell with a CoMn₂O₄/NC air cathode achieved a peak power density of 23.72 W m^?2, which was even superior to that with a commercial Pt/C air cathode. This work revealed that ionic liquid is a viable reaction medium for preparation of catalyst with robust activity.