Highly Efficient Methanol Oxidation Reaction Achieved by Cobalt Doping in Delafossite AgNi_1–xCo_xO₂ Solid Solution

Abstract

Developing highly active and durable non-platinum catalysts for methanol oxidation is of great significance for direct methanol fuel cells. However, their electrocatalytic efficiency is still insufficient mainly due to their poor electrical conductivity and slow reaction kinetics. Herein, a non-Pt electrocatalyst AgNi 0.8 Co 0.2 O 2 with a delafossite structure is facilely constructed via a cation-exchange strategy for the methanol oxidation reaction in alkaline media. The introduction of Co atoms is favorable to crystallization for boosting the synthesis procedure. Meanwhile, the uniform distribution of Co and Ni in the structure brings about additional oxygen vacancies in the materials, thereby improving the intrinsic methanol oxidation reaction activity of the catalysts, and the introduced Co atoms can help to oxidize intermediates such as formaldehyde. Therefore, the electrocatalyst exhibits excellent electrocatalytic performance (77.6 mA cm −2 , 220 mA mg −1 ) and high selectivity, and it can effectively inhibit the oxygen evolution reaction (310 mV difference from the oxygen evolution reaction potential at 10 mA cm −2 ). This work not only provides a material system using cheap and effective non-Pt catalysts based on Ag-based delafossite oxides but also sheds light on the engineering of oxygen vacancies of electrocatalysts for developing highperformance direct methanol fuel cells.

Gram-scale solvothermal synthesis of Fe-doped CuCoO2 nanosheets and improvement of the oxygen evolution reaction performance

“…The Ni@3FCCO electrode exhibits the lowest Tafel slopes of 69 mV dec −1 , the lower Tafel slope value indicates that achieving the same current density requires a lower overpotential, which proves that the OER kinetics of the Ni@3FCCO electrode is the fastest. The required overpotential to obtain a current density of 10 mA cm −2 and the Tafel slope of Ni@3FCCO electrode are both superior to or close to some non-noble metal oxide catalysts reported in the literature (Table S2†), such as delafossite oxides, including CuScO 2 ( η 10 = 470 mV, Tafel slope = 114 mV dec −1 ), 26 AgCoO 2 ( η 10 = 395 mV), 60 AgNi 0.8 Co 0.2 O 2 ( η 10 = 310 mV), 29 CuFeO 2 (Tafel slope = 49.4 mV dec −1 ), 15 CuCoO 2 ( η 10 = 440 mV, Tafel slope = 92.8 mV dec −1 ), 19 Ca doped CuCoO 2 ( η 10 = 470 mV, Tafel slope = 96.5 mV dec −1 ), 30 Ni doped CuCoO 2 ( η 10 = 470 mV, Tafel slope = 96.5 mV dec −1 ); 35 or other perovskite electrocatalysts, including LaFeO 3 ( η 10 = 420 mV, Tafel slope = 62 mV dec −1 ), 61 LaNiO 3 ( η 10 = 550 mV, Tafel slope = 148 mV dec −1 ), 62 LaNi 0.85 Mg 0.15 O 3 ( η 10 = 450 mV, Tafel slope = 95 mV dec −1 ), 62 LaNiO 3 ( η 10 = 460 mV, Tafel slope = 96 mV dec −1 ), 63 LaCo 0.30 Rh 0.70 O 3 ( η 10 = 470 mV, Tafel slope = 126 mV dec −1 ), 64 and La 1− x Sr x CoO 3− δ ( η 10 = 326 mV, Tafel slope = 70.8 mV dec −1 ). 65…”

“…In practice, the effectiveness of this concept has been well demonstrated in some recent reports. For example, Zhang et al 29 introduced the Co element into delafossite AgNiO 2 which not only promoted the formation of oxygen vacancies, but also improved the catalytic activity of the catalyst ( η 10 = 310 mV). Du et al 30 introduced the Ca element in CuCoO 2 which reduced the grain size and increased the specific surface area, thereby increasing the electrocatalytically active area and significantly increasing the OER catalytic performance ( η 10 = 470 mV).…”

Unveiling the Mechanistic Significance of Reducibility and Lattice Oxygen Evolution in the Ce1–x–yZrxNiyO2−δ Catalyst for Methanol Electro-Oxidation

“…The CV traces in an alkaline solution without methanol in Figure a show almost no significant peak in the case of pristine CeO 2 and a prominent anodic peak at 1.43 V versus RHE and a counter cathodic peak at 1.36 V versus RHE in the doped materials. The anodic peak may correspond to the formation of oxyhydroxide (–OOH) species associated with the oxidation of higher valency Ni, while the counter cathodic peak might be associated with the corresponding reduction process of Ni–OOH, suggesting a redox Ni 2+ /Ni 3+ process in the experimental potential window. ,,− Formation of a thicker layer of –OOH with Ni 3+ was further supported when the corresponding peak current density increased gradually with the increase in the scan rate from 10 to 100 mVs –1 (Figure S5) over the doped materials. It was interesting to observe that the surface concentration of –OOH species was higher in Ce 0.95 Ni 0.05 O 2−δ than that in Zr 0.95 Ni 0.05 O 2−δ .…”

Promoting the four electrocatalytic reactions of OER/ORR/HER/MOR using a multi-component metal sulfide heterostructure for zinc-air batteries and water-splitting

“…Evidently, the ECSA of Co-S-INF was much higher than that of INF-S, which can be attributed to its plentiful catalytic sites by introducing the Co sulfide and nano-sheet microstructure. 47 Co-S-INF undergoes a CP test toward MOR in 1.0 M KOH + 1.0 M methanol mixed solution at a current density of 100 mA cm −2 for 27 h (Fig. 4h), manifesting its good stability toward MOR.…”