Alternative Strategy for Development of Dielectric Calcium Copper Titanate‑Based Electrolytes for Low‑Temperature Solid Oxide Fuel Cells

The development of low-temperature solid oxide fuel cells(LT-SOFCs)is of significant importance for realizing the widespread application of SOFCs.This has stimulated a substantial materials research effort in developing high oxide-ion conductivity in the electrolyte layer of SOFCs.In this context,for the first time,a dielectric material,CaCu_(3)Ti_(4)O_(12)(CCTO)is designed for LT-SOFCs electrolyte application in this study.Both individual CCTO and its heterostructure materials with a p-type Ni_(0.8)Co_(0.15)Al_(0.05)LiO_(2−δ)(NCAL)semiconductor are evaluated as alternative electrolytes in LT-SOFC at 450–550℃.The single cell with the individual CCTO electrolyte exhibits a power output of approximately 263 mW cm^(-2) and an open-circuit voltage(OCV)of 0.95 V at 550℃,while the cell with the CCTO–NCAL heterostructure electrolyte capably delivers an improved power output of approximately 605 mW cm^(-2) along with a higher OCV over 1.0 V,which indicates the introduction of high hole-conducting NCAL into the CCTO could enhance the cell performance rather than inducing any potential short-circuiting risk.It is found that these promising outcomes are due to the interplay of the dielectric material,its structure,and overall properties that led to improve electrochemical mechanism in CCTO–NCAL.Furthermore,density functional theory calculations provide the detailed information about the electronic and structural properties of the CCTO and NCAL and their heterostructure CCTO–NCAL.Our study thus provides a new approach for developing new advanced electrolytes for LT-SOFCs.

Highly Active Interfacial Sites in SFT-SnO_(2) Heterojunction Electrolyte for Enhanced Fuel Cell Performance via Engineered Energy Bands:Envisioned Theoretically and Experimentally

Extending the ionic conductivity is the pre-requisite of electrolytes in fuel cell technology for high-electrochemical performance.In this regard,the introduction of semiconductor-oxide materials and the approach of heterostructure formation by modulating energy bands to enhance ionic conduction acting as an electrolyte in fuel cell-device.Semiconductor(n-type;SnO_(2))plays a key role by introducing into p-type SrFe_(0.2)Ti_(0.8)O_(3-δ)(SFT)semiconductor perovskite materials to construct p-n heterojunction for high ionic conductivity.Therefore,two different composites of SFT and SnO_(2)are constructed by gluing p-and n-type SFT-SnO_(2),where the optimal composition of SFT-SnO_(2)(6∶4)heterostructure electrolyte-based fuel cell achieved excellent ionic conductivity 0.24 S cm^(-1)with power-output of 1004 mW cm^(-2)and high OCV 1.12 V at a low operational temperature of 500℃.The high power-output and significant ionic conductivity with durable operation of 54 h are accredited to SFT-SnO_(2)heterojunction formation including interfacial conduction assisted by a built-in electric field in fuel cell device.Moreover,the fuel conversion efficiency and considerable Faradaic efficiency reveal the compatibility of SFT-SnO_(2)heterostructure electrolyte and ruled-out short-circuiting issue.Further,the first principle calculation provides sufficient information on structure optimization and energy-band structure modulation of SFT-SnO_(2).This strategy will provide new insight into semiconductor-based fuel cell technology to design novel electrolytes.

A Bulk‑Heterostructure Nanocomposite Electrolyte of Ce_(0.8)Sm_(0.2)O_(2‑δ)-SrTiO_(3) for Low‑Temperature Solid Oxide Fuel Cells

Since colossal ionic conductivity was detected in the planar heterostructures consisting of fluorite and perovskite,heterostructures have drawn great research interest as potential electrolytes for solid oxide fuel cells(SOFCs).However,so far,the practical uses of such promising material have failed to materialize in SOFCs due to the short circuit risk caused by SrTiO3.In this study,a series of fluorite/perovskite heterostructures made of Sm-doped CeO2 and SrTiO3(SDC–STO)are developed in a new bulk-heterostructure form and evaluated as electrolytes.The prepared cells exhibit a peak power density of 892 mW cm−2 along with open circuit voltage of 1.1 V at 550°C for the optimal composition of 4SDC–6STO.Further electrical studies reveal a high ionic conductivity of 0.05–0.14 S cm^−1 at 450–550°C,which shows remarkable enhancement compared to that of simplex SDC.Via AC impedance analysis,it has been shown that the small grain-boundary and electrode polarization resistances play the major roles in resulting in the superior performance.Furthermore,a Schottky junction effect is proposed by considering the work functions and electronic affinities to interpret the avoidance of short circuit in the SDC–STO cell.Our findings thus indicate a new insight to design electrolytes for low-temperature SOFCs.

Novel LaFe_(2)O_(4)spinel structure with a large oxygen reduction response towards protonic ceramic fuel cell cathode

Highly active and stable electrocatalysts are mandatory for developing high-performance and longlasting fuel cells.The current study demonstrates a high oxygen reduction reaction(ORR)electrocatalytic activity of a novel spinel-structured LaFe_(2)O_(4)via a self-doping strategy.The LaFe_(2)O_(4)demonstrates excellent ORR activity in a protonic ceramic fuel cell(PCFC)at temperature range of 350-500℃.The high ORR activity of LaFe_(2)O_(4)is mainly attributed to the facile release of oxide and proton ions,and improved synergistic incorporation abilities associated with interplay of multivalent Fe^(3+)/Fe^(2+)and La^(3+)ions.Using LaFe_(2)O_(4)as cathode over proton conducting BaZr_(0.4)Ce_(0.4)Y_(0.2)O_(3)(BZCY)electrolyte,the fuel cell has delivered a high-power density of 806 mW/cm^(2)operating at 500℃.Different spectroscopic and calculations methods such as UV-visible,Raman,X-ray photoelectron spectroscopy and density functional theory(DFT)calculations were performed to screen the potential application of LaFe_(2)O_(4)as cathode.This study would help in developing functional cobalt-free ORR electrocatalysts for low temperature-PCFCs(LT-PCFCs)and solid oxide fuel cells(SOFCs)applications.

Semiconductor Electrochemistry for Clean Energy Conversion and Storage

Semiconductors and the associated methodologies applied to electrochemistry have recently grown as an emerging field in energy materials and technologies.For example,semiconductor membranes and heterostructure fuel cells are new technological trend,which differ from the traditional fuel cell electrochemistry principle employing three basic functional components:anode,electrolyte,and cathode.The electrolyte is key to the device performance by providing an ionic charge flow pathway between the anode and cathode while preventing electron passage.In contrast,semiconductors and derived heterostructures with electron(hole)conducting materials have demonstrated to be much better ionic conductors than the conventional ionic electrolytes.The energy band structure and alignment,band bending and built-in electric field are all important elements in this context to realize the necessary fuel cell functionalities.This review further extends to semiconductor-based electrochemical energy conversion and storage,describing their fundamentals and working principles,with the intention of advancing the understanding of the roles of semiconductors and energy bands in electrochemical devices for energy conversion and storage,as well as applications to meet emerging demands widely involved in energy applications,such as photocatalysis/water splitting devices,batteries and solar cells.This review provides new ideas and new solutions to problems beyond the conventional electrochemistry and presents new interdisciplinary approaches to develop clean energy conversion and storage technologies.

Proton transport controlled at surface layer of CeO_(2) by gradient-doping with a built-in-field effect

Ceramic fuel cells hold an important position for the sustainable energy future using renewable energy sources with high efficiency.The design and synthesis of active materials,interface engineering and having capability of low operating temperature is considered as an important factor to further increase the power output and stability of ceramic fuel cell devices.A novel methodology has vital importance to develop new functionalities of existing materials by introducing new different effects.The built-in electric field(BIEF) is one of the most recently used approaches to improve charge transfer and ionic conductivity of solid oxide materials.Herein,we demonstrate gradient doping strategy in CeO_(2)-δstructure to produce BIEF effect and to modulate the proton transport effectively at the surface layer rather than bulk structure.The inclusions of La and Sr metal ions at the surface and Co-metal ions into bulk-layer of CeO_(2)form the gradiently doped structure.The gradient doping into CeO_(2)highly improves the proton transport properties through the surface layer by modifying the energy levels.Moreover,unbalanced charge distribution due to gradient doping produces built-in electric-field to provide extra driving force for protons transport through surface layer.The acquired gradiently doped fluorite structure exhibits remarkable proton conductivity of>0.2 S/cm,as a result ceramic fuel cell shows power output of>1000 mW/cm2while operating at 500℃.This unique work highlights the critical role of gradiently doped electrolyte in electrochemical conversion energy devices and offers new understanding and practices for sustainable energy future.