The oxygen evolution reaction (OER) is an essential reaction for the sustainable synthesis of fuels from renewable feedstocks. In recent years, cathode materials for Li-ion batteries have been successfully utilized as OER electrocatalysts, and among them are the lithiated transition-metal phosphates possessing an olivine crystallographic phase. The LiMPO₄ (M = Ni, Fe, Co) olivine materials display a potentially suitable overpotential for OER, which can be further enhanced by delithiation. Herein, we report the synthesis of olivine phases with both Li and Na as alkaline ions. The combination of alkaline ions stabilizes the olivine structure with low alkaline ion content, which is instrumental to reach low OER overpotential. The dual alkaline ion approach has been demonstrated for a single transition metal (Co) as well as different combinations of Co–Fe–Ni to form olivine solid solutions of the chemical formula Li(Na)Co(Fe,Ni)PO₄. This screening of eight olivine materials revealed a trend in OER activity, and the Li_0.6Na_0.2Ni_0.7Fe_0.1PO₄ solid solution displays an overpotential as low as 0.28 V versus RHE at 10 mA cm^–2, with a low Tafel slope of 30 mV dec^–1 and a stability tested over 20 h.

中文翻译：

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氧气逸出橄榄石电催化剂中化学去插入的双碱性离子途径

氧气析出反应（OER）是从可再生原料可持续合成燃料的必不可少的反应。近年来，已经成功地将用于锂离子电池的正极材料用作OER电催化剂，其中包括具有橄榄石结晶相的锂化过渡金属磷酸盐。LiMPO ₄（M = Ni，Fe，Co）橄榄石材料显示出可能适合OER的过电势，可以通过脱锂进一步增强。本文中，我们报道了以Li和Na为碱性离子的橄榄石相的合成。碱性离子的结合以低碱性离子含量稳定了橄榄石结构，这有助于达到较低的OER过电位。已经证明了双碱性离子方法可用于单一过渡金属（Co）以及Co-Fe-Ni的不同组合，以形成化学式为Li（Na）Co（Fe，Ni）PO _4的橄榄石固溶体。对八种橄榄石材料的筛选显示了OER活性的趋势，以及Li _0.6 Na _0.2 Ni _0.7 Fe _0.1 PO _4的趋势固溶体在10 mA cm ^–2时相对于RHE的过电势低至0.28 V ，Tafel斜率低，dec ^–1为30 mV ，经过20 h的稳定性测试。