Facile Access to an Active γ‐NiOOH Electrocatalyst for Durable Water Oxidation Derived From an Intermetallic Nickel Germanide Precursor

Abstract

Identifying novel classes of precatalysts for the oxygen evolution reaction (OER by water oxidation) with enhanced catalytic activity and stability is a key strategy to enable chemical energy conversion. The vast chemical space of intermetallic phases offers plenty of opportunities to discover OER electrocatalysts with improved performance. Herein we report intermetallic nickel germanide (NiGe) acting as a superior activity and durable Ni‐based electro(pre)catalyst for OER. It is produced from a molecular bis(germylene)‐Ni precursor. The ultra‐small NiGe nanocrystals deposited on both nickel foam and fluorinated tin oxide (FTO) electrodes showed lower overpotentials and a durability of over three weeks (505 h) in comparison to the state‐of‐the‐art Ni‐, Co‐, Fe‐, and benchmark NiFe‐based electrocatalysts under identical alkaline OER conditions. In contrast to other Ni‐based intermetallic precatalysts under alkaline OER conditions, an unexpected electroconversion of NiGe into γ‐NiIIIOOH with intercalated OH−/CO32− transpired that served as a highly active structure as shown by various ex situ methods and quasi in situ Raman spectroscopy.

Strategies and Perspectives to Catch the Missing Pieces in Energy‐Efficient Hydrogen Evolution Reaction in Alkaline Media

“…Alkaline water electrolysis, in contrast, is blessed with a vast variety of non‐precious electrocatalysts for OER that include hydroxides/oxyhydroxides, oxides, chalcogenides, pnictides, carbides, borides and intermetallics. [ 17 , 28 , 42 , 43 , 44 , 45 ] Among them, those non‐oxide/hydroxide catalysts are recently comprehended to act as precatalysts rather than actual OER catalysts because of the lability of non‐oxide/hydroxide anions that are easily displaced by hydroxide anion under highly alkaline solution. [ 46 , 47 , 48 , 49 ] Such a displacement of non‐oxide/hydroxide anions occurs even under reductive potentials in alkaline solutions.…”

Intermetallic Fe6Ge5 formation and decay of a core–shell structure during the oxygen evolution reaction

“…10 Herein, we report on the first iron-based OER catalyst containing germanium, intermetallic Fe 6 Ge 5 , and uncover its structural transformation during the OER. 11,12 Intermetallic Fe 6 Ge 5 was synthesized using a high-temperature annealing method (details in the ESI †). It crystallises in its own structure derived from the B8 type (Fig.…”

Recent Progress on Structurally Ordered Materials for Electrocatalysis

“…i) Quasi in situ and ex situ Raman spectroscopy of NiGe on fluorinated tin oxide collected at a potential of 1.58 V. Reproduced with permission. [ 51 ] Copyright 2021, Wiley‐VCH.…”

“…For example, intermetallic NiGe deposited on both nickel foam and fluorinated tin oxide electrodes exhibited superior OER activity and stability (over three weeks) to those of state‐of‐the‐art Ni‐, Co‐, Fe‐, and benchmark NiFe‐based electrocatalysts. [ 51 ] γ‐NiOOH with intercalated OH − /CO 3 2− , which was electrochemically transformed from NiGe, was found to act as the true active species from combined ex situ characterizations and quasi in situ Raman spectroscopy (Figure 4h,i).…”