Sintering aids for proton-conducting oxides – A double-edged sword? A mini review

•A brief history of using sintering aids for proton-conducting oxides is presented.•Whether the electrochemical performance is influenced by sintering aids is discussed.•Prospects and possible solutions are discussed. Sintering aids are often used in the fabrication of proton-conducting oxides to facilitate their application in solid oxide cells, but the detrimental effects of sintering aids on electrochemical performance have been noted in early studies. However, the landscape has changed as some recent studies have suggested that overall electrochemical performance is actually enhanced by using sintering aids, making this an important topic for debate. This mini review presents a discussion of the influence of sintering aids on the electrochemical performance of proton-conducting oxides, considering older studies as well as more recent results. The merits and challenges of sintering-aid-modified proton-conducting oxides are discussed.