Progress and challenges of carbon-fueled solid oxide fuel cells anode

Carbon-fueled solid oxide fuel cells(CF-SOFCs)can electrochemically convert the chemical energy in carbon into electricity,which demonstrate both superior electrical efficiency and fuel utilisation compared to all other types of fuel cells.However,using solid carbon as the fuel of SOFCs also faces some challenges,the fluid mobility and reactive activity of carbon-based fuels are much lower than those of gaseous fuels.Therefore,the anode reaction kinetics plays a crucial role in determining the electrochemical performance of CF-SOFCs.Herein,the progress of various anodes in CF-SOFCs is reviewed from the perspective of material compositions,electrochemical performance and microstructures.Challenges faced in developing high performance anodes for CF-SOFCs are also discussed.

Transition Metal Doped MnO_x-CeO₂Catalysts by Ultrasonic Immersing for Selective Catalytic Reduction of NO with NH₃at Low Temperature

Transition metals doped Mn-based catalysts were prepared via ultrasonic immersing method for the selective catalytic reduction (SCR) of NOx from fuel gas. The Catalysts’ DeNOx efficiency and tolerance to sulfur were investigated in the paper. XRD results demonstrate high dispersion of Mn, Ce and M (Pr, Y, Zr, W) elements on TiO2 carrier, which is favor for reduction of active materials content. Mn-Ce-W catalyst presents uniform particle size about 500 nm to 800 nm from SEM pictures and shows the best NOx conversion of 93.2% at 200°C and 98.4% at 250°C, respectively. Sulfur tolerance analysis indicated that transition metals M can improve the catalysts’ performance when 0.01% SO2 exists in the fuel gas, because metal doping into the Mn-Ce catalyst can inhibit the sulfate deposition, especially metal sulfate, on the catalyst, which can be seen from the Fourier infrared spectrum.

Barium-doped Pr_(2)Ni_(0.6)Cu_(0.4)O_(4+δ) with triple conducting characteristics as cathode for intermediate temperature proton conducting solid oxide fuel cell

Proton conducting solid oxide fuel cell(H-SOFC)is an emerging energy conversion device,with lower activation energy and higher energy utilization efficiency.However,the deficiency of highly active cathode materials still remains a major challenge for the development of H-SOFC.Therefore,in this work,K_(2)NiF_(4)-type cathode materials Pr_(2-x)Ba_(x)Ni_(0.6)Cu_(0.4)O_(4+δ)(x=0,0.1,0.2,0.3),single-phase tripleconducting(e-/O^(2-)/H^(+))oxides,are prepared for intermediate temperature H-SOFCs and exhibit good oxygen reduction reaction activity.The investigation demonstrates that doping Ba into Pr_(2-x)BaxNi_(0.6)Cu_(0.4)O_(4+δ) can increase its electrochemical performance through enhancing electrical conductivity,oxygen vacancy concentration and proton conductivity.EIS tests are carried at 750℃ and the minimum polarization impedances are obtained when x=0.2,which are 0.068 Ω·cm^(2) in air and 1.336 Ω·cm^(2) in wet argon,respectively.The peak power density of the cell with Pr_(1.8)Ba_(0.2)Ni_(0.6)Cu_(0.4)O_(4+δ) cathode is 298 mW·cm^(-2) at 750℃ in air with humidified hydrogen as fuel.Based on the above results,Ba-doped Pr_(2-x)Ba_(x)Ni_(0.6)Cu_(0.4)O_(4+δ) can be a good candidate material for SOFC cathode applications.

High-entropy perovskite oxide BaCo_(0.2)Fe_(0.2)Zr_(0.2)Sn_(0.2)Pr_(0.2)O_(3-δ) with triple conduction for the air electrode of reversible protonic ceramic cells

Reversible protonic ceramic cells(RPCCs) show great potential as new-generation energy conversion and storage devices. However, the mature development of RPCCs is seriously hindered by the inactivity and poor stability of air electrodes exposed to concentrated vapor under operating conditions. Herein, we report a high-entropy air electrode with the composition BaCo_(0.2)Fe_(0.2)Zr_(0.2)Sn_(0.2)Pr_(0.2)O_(3-δ)(BCFZSP), which shows integrated electronic, protonic and oxygenic conduction in a single perovskite phase and excellent structural stability in concentrated steam. Such triple conduction can spread the electrochemically active sites of the air electrode to the overall electrode surface, thus optimizing the kinetics of the oxygen reduction and evolution reactions(0.448 Ω cm^(2) of polarization resistance at 550℃). As-prepared RPCCs with a BCFZSP air electrode at 600℃ achieved a peak power density of 0.68 W/cm^(2) in fuel-cell mode and a current density of 0.92 A/cm^(2) under a 1.3 V applied voltage in electrolysis mode. More importantly, the RPCCs demonstrate an encouragingly high stability during 120 h of reversible switching between the fuelcell and electrolysis modes. Given their excellent performance, high-entropy perovskites can be promising electrode materials for RPCCs.

Balancing particle properties for practical lithium-ion batteries

As a state-of-the-art secondary battery,lithium-ion batteries(LIBs)have dominated the consumer electronics market since Sony unveiled the commercial secondary battery with LiCoO_(2) as the negative electrode material in the early 1990s.The key to the efficient operation of LIBs lies in the effective contact between the Li-ion-rich electrolyte and the active material particles in the electrode.The particle properties of the electrode materials affect the lithium ion diffusion path,diffusion resistance,contact area with the active material,the electrochemical performance and the energy density of batteries.To achieve satisfied comprehensive performance and of LIBs,it is not only necessary to focus on the modification of materials,but also to balance the properties of electrode material particles.Therefore,in this review,we analyze the influence of particle properties on the battery performance from three perspectives:particle size,particle size distribution,and particle shape.A deep understanding of the effect and mechanism of particles on electrodes and batteries will help develop and manufacture practical LIBs.

Sn and Y co-doped BaCo_(0.6)Fe_(0.4)O_(3)-δcathodes with enhanced oxygen reduction activity and CO_(2) tolerance for solid oxide fuel cells

Applying mixed oxygen ionic and electronic conducting(MIEC)oxides as the cathode offers a promis-ing solution to enhance the performance of solid oxide fuel cells(SOFCs).However,the phase instability in CO_(2)-containing air and sluggish oxygen reduction activity of MIEC cathodes remain a long-term chal-lenge for optimizing the electrochemical performance of SOFCs.Herein,a heterovalent co-doping strategy is proposed to enhance the oxygen reduction activity and CO_(2)tolerance of SOFCs cathodes,which can be demonstrated by developing a novel BaCo_(0.6)Fe_(0.4)O_(3)-δ(BCF)-based MIEC oxide,BaCo_(0.6)Fe_(0.2)Sn_(0.1) Y_(0.1)O_(3-δ)(BCFSY).In addition to improving the stability of BCF-based perovskites,this strategy achieves an opti-mized balance of ionic mobility and oxygen vacancies due to the synergies between the effects of the co-dopants.Compared with single-doped materials,BCFSY exhibits improved CO_(2)tolerance and consider-ably higher ORR activity,which is reflected in a significantly lower polarization resistance of 0.15Ωcm^(2) at 600℃.The results of this work provide an efficient tactic for designing electrode materials for SOFCs.

Spinel-type bimetal sulfides derived from Prussian blue analogues as efficient polysulfides mediators for lithium-sulfur batteries

More and more attentions have been attracted by lithium-sulfur batteries(Li-S), owing to the high energy density for the increasingly advanced energy storage system. While the poor cycling stability, due to the inherent polysulfide shuttle, seriously hampered their practical application. Recently, some polar hosts,like single metal oxides and sulfides, have been employed as hosts to interact with polysulfide intermediates. However, due to the inherent poor electrical conductivity of these polar hosts, a relatively low specific capacity is obtained. Herein, a spinel-type bimetal sulfide NiCo_(2)S_(4)through a Prussian blue analogue derived methodology is reported as the novel host of polysulfide, which enables highperformance sulfur cathode with high Coulombic efficiency and low capacity decay. Notably, the Li-S battery with NiCo_(2)S_(4)-S composites cathode still maintains a capacity of 667 m Ah/g at 0.5 Cafter 300 cycles, and 399 m Ah/g at 1 C after 300 cycles. Even after 300 cycles at the current density of 0.5C, the capacity decays by 0.138% per cycle at high sulfur loading about 3 mg/cm;. And the capacity decays by0.026% per cycle after 1000 cycles, when the rate is 1C. More importantly, the cathode of Ni Co_(2)S_(4)-S composite shows the outstanding discharge capacity, owing to its good conduction, high catalytic ability and the strong confinement of polysulfides.

Fluorination Intensifying Oxygen Evolution Reaction for High-Temperature Steam Electrolysis

Solid oxide electrolysis cells(SOECs)have emerged as one of the most potent techniques for hydrogen production.As the restricted step for SOEC,as well as the most predominant obstacle to the scaled application,oxygen evolution reaction(OER)should be urgently accelerated by developing potent electrocatalysts.Despite inferior electrochemical activity to cobalt-based materials,perovskite ferrites exhibit great potential in the future with regard to good intrinsic stability and durability,abundant reserves,and good compatibility with other SOEC components.In this work,fluorination is introduced to the typical perovskite ferrite to further intensify the OER process.Ab initio calculations combined with physical-chemical characterizations are performed to reveal the mechanism.The doped F^(−)leads to debilitating the strength of the metal-oxygen bond and then reduces the energy for oxygen vacancy formation and ion migration,which renders improvements to sub-processes of OER on the anode.The well-verified material,PrBaFe_(2)O_(5+δ)F_(0.1)(PBFOF),exhibited a low polarization resistance of 0.058Ωcm^(-2).Single cells based on PBFOF showed a high current density of 2.28 A cm^(-2) at 750°C under 1.3 V.This work provides a clear insight into the mechanism of fluorination on perovskites and high-activity anode material for SOEC.