Nanostructured Ball-Milled Ni–Co–Mn Oxides from Spent Li-Ion Batteries as Electrocatalysts for Oxygen Evolution Reaction

Abstract

Discovering sources of transition metals, such as Ni, Co, and Mn, has become crucial due to their broad applicability, particularly as electrocatalysts for the oxygen evolution reaction (OER). Upcycled spent batteries have emerged as alternatives for transition metal sources for the OER electrocatalysts. In this work, Ni−Co−Mn oxalates were extracted from the spent LiNi x Co y Mn z O 2 (NCM) cathode of lithium-ion batteries. The extracted oxalates were further processed via ball milling as a rapid and scalable mechanochemical route to engineer their structures. After calcination, Ni−Co−Mn oxides with nanosized granules on the surface that mainly consist of MnCo 2 O 4 were obtained. With a correlation of morphology and trimetallic oxide formation with the OER catalytic performance, Ni−Co−Mn oxides exhibit OER overpotentials of 367 and 732 mV in alkaline and neutral media, respectively, showing OER catalytic activity in a wide pH range. The results indicate that ball milling can induce particle size reduction and bond formation between metals to facilitate mixedmetal oxide formation. Furthermore, the resulting material is also applicable as the catalyst in the air cathode of Zn-air batteries, where the battery achieved a power density of 85.42 mW cm −2 and 100 h of cycling stability, showing comparability with a battery with a Pt/C−Ir/C catalyst.

Avoid Using Phosphate Buffered Saline (PBS) as an Electrolyte for Accurate OER Studies

“…The prevalent use of “0.1/1 M PBS” in the water electrolysis community often lacks composition details, − with “PBS” sometimes being used without specifying its full name. − This leads to misinformation within the water electrolysis community, as it could either denote pure phosphate buffer solution − or phosphate buffered saline, − which have different salt compositions, ionic strengths and ionic conductivities. Such lack of clarity poses complication and misinformation during cross-referencing among researchers. , Furthermore, denoting concentration using molarity is only correct for pure phosphate buffer solution, but not for phosphate buffered saline.…”