State-of-the-Art Iridium-Based Catalysts for Acidic Water Electrolysis: A Minireview of Wet-Chemistry Synthesis Methods

Abstract

With the increasing demand for clean hydrogen production, both as a fuel and an indispensable reagent for chemical industries, acidic water electrolysis has attracted considerable attention in academic and industrial research. Iridium is a well-accepted active and corrosion-resistant component of catalysts for oxygen evolution reaction (OER). However, its scarcity demands breakthroughs in catalyst preparation technologies to ensure its most efficient utilization. This minireview focusses on the wet-chemistry synthetic methods of the most active and (potentially) durable Ir catalysts for acidic OER, selected from the recent publications in the open literature. The catalysts are classified by their synthesis methods, with authors' opinion on their practicality. The review may also guide the selection of the state-of-the-art Ir catalysts for benchmarking purposes.

Comparative Analysis of Synthesis Routes for Antimony‐Doped Tin Oxide‐Supported Iridium and Iridium oxide Catalysts for OER in PEM Water Electrolysis

“…Higher crystallinity of IrO 2 increases its electrochemical stability but also dampens activity. [ 19,21 ] The chosen temperature at 375 °C, as suggested by Böhm et al., does seem to invoke the majority of Ir oxidation, while preserving low crystallinity of IrO 2 , improving its electrochemical activity, and preserving disperse small particles to improve activity even further. [ 8 ] Trends observed in the high‐temperature diffractograms can also be seen in thermally treated catalysts, with Ir(111) narrowing and the emergence of IrO 2 reflexes in calcined RS catalysts.…”

“…With MAF employing a salt melt using only readily available NaNO 3 , this method can be easily adapted to industrial processes. [ 19 ] Catalyst properties like particle size and crystallinity are also easily modifiable by temperature variation. In contrast, the other methods employ a wet chemical approach that can increase complexity and may require the substitution of solvents or additives at high scales.…”

“…Metallic Ir catalysts are electrochemically oxidized under operation conditions to form a mixed oxide IrO x layer. [19,20] This species shows the highest activity toward oxygen evolution reaction (OER); however, it exhibits performance decay, due in part to lattice defects. On the other hand, thermally treated Ir is converted to crystalline tetragonal IrO 2 and shows enhanced stability, especially during long-term operation, but lower performance.…”

“…On the other hand, thermally treated Ir is converted to crystalline tetragonal IrO 2 and shows enhanced stability, especially during long-term operation, but lower performance. [19,[21][22][23] In addition to the oxidation state of Ir, several other factors are influenced by the synthesis, such as Ir particle dispersion and size. Scalability of reaction schemes for industrial applications and efficiency regarding Ir deposition yield influence the choice of synthesis route.…”

Toward efficient electrocatalytic oxygen evolution with a low concentration baking soda activated IrOxsurface in a hydrothermal medium

“…6 Many efforts have been devoted to developing advanced Irbased catalysts and searching the key factors related to OER performance at Ir sites by precise structural characterizations and sophisticated theoretical calculations. Natalia et al, 7 Duan et al, 8,9 Wang et al 10 and Zhao et al 11 summarized in detail the recent progress of Ir-based catalysts and also gave meaningful guidance for subsequent studies. Moreover, Camila et al 12 had done quantitative benchmarking work on IrO x to deduce a selection of suitable catalysts for diminishing the cost of PEM; Marion et al 13 based on amorphous IrO x revealed that surface structural features have a greater effect on OER activity than the iridium oxidation state.…”