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Page 2 of 11 Chen et al. Energy Mater 2022;2:200033 https://dx.doi.org/10.20517/energymater.2022.36

INTRODUCTION
Noble metals, especially Pt, are well known to be excellent oxygen reduction reaction (ORR) catalysts for
fuel cells. However, Pt reserves are so limited that it is necessary to improve the specific mass activity of Pt.
The universal ORR volcano curve indicates that decreasing the oxygen adsorption energy of Pt helps to
[1]
improve its ORR catalysis performance and Pt-based catalysts have been a popular research topic in recent
[2-4]
[5-8]
years . Alloying Pt with Cu is a useful strategy to reach this goal because the strain and electron effects
of Cu doping help to modify Pt [9,10] . For traditional Pt catalysts, porous carbon is used as a carrier to improve
the surface area and conductivity of the catalysts. However, the carbon corrosion reaction of the carrier
makes it challenging to apply Pt catalysts in practical fuel cells . The construction of noble metals and their
[11]
alloys as aerogels not only helps in avoiding the carbon corrosion reaction in fuel cells but also enlarges the
specific surface areas and increases the porosity of the materials. Consequently, this approach improves the
mass and electron transfer and thus enhances the electrocatalytic activities.

Noble metal aerogels (NMAs) originated from Eychmüller’s group in 2009 . They proposed a two-step sol-
[12]
gel process to fabricate non-supported macroscopic aerogels. During early development, the route was not
[12]
satisfactory because gelation took a long period of 1-4 weeks . In recent years, researchers have developed
the gelation process with a number of strategies, including cation and salt-inducing effects [14-21] and the
[13]
use of external factors, like heating and stirring , thereby shortening the time significantly to several
[23]
[22]
hours. For higher efficiency, one-step methods have also been proposed, where the reduction and gelation
take place in one pot without any other stabilizer or initiator [22-35] . The enhanced kinetics of these methods
benefit the fabrication of aerogels. Among the many known aerogels, there are only a few with ORR
catalytic activity, thereby inspiring us to develop appropriate catalysts for the ORR.

In this work, we demonstrate a facile one-step method for preparing Pt-based aerogels and develop PtCu
aerogels with excellent electrochemical catalysis toward the ORR. Sodium chloroplatinate (Na PtCl ) and
4
2
copper chloride (CuCl ) are reduced by NaBH , which acts not only as a reductant but also as a stabilizer
4
2
and initiator, at room temperature. The PtCu aerogels are formed in tens of minutes and can be obtained
after standing for several hours. The as-prepared PtCu aerogels exhibit a hierarchically porous structure
with a high specific area of 33.0 m /g, and an outstanding ORR activity with a mass activity of 369.4
2
2
mA/mg and a specific activity of 0.847 mA/cm , which were 2.6 and 3.3 times greater than those of
Pt
commercial Pt/C, respectively. The PtCu aerogels in this work are among the best Pt-based aerogel ORR
catalysts that have been reported.
EXPERIMENTAL
Chemicals
Sodium chloroplatinate (Na PtCl ) was provided by Sino-Platinum Metals Co., Ltd. Copper chloride
4
2
dihydrate (CuCl ·2H O), trisodium citrate dihydrate (C H Na O ·2H O), anhydrous ethanol and methanol
5
7
2
2
3
8
2
were purchased from Sinopharm Chemical Reagent Co., Ltd. All materials were of analytical reagent grade
and used as received. Ultrapure water (18.25 mΩ·cm) from an ULUPURE UPH-III-10 water purifier was
used throughout the experiments.
Synthesis of PtCu aerogels
In a typical synthesis of the PtCu aerogels, Na PtCl (685 μL, 5 × 10 mol) and CuCl (200 μL, 5 × 10 mol)
-5
-5
2
2
4
were dissolved in ultrapure water in a 50 mL centrifuge tube to obtain an aqueous solution of 20 mL.
-3
Following that, a fresh NaBH (5 mL, 2 × 10 mol) aqueous solution was shaken for several seconds and
4
added to the tube at room temperature. The formation process of the PtCu aerogels is shown in Figure 1. In
the first few minutes, a single black foam quickly formed and floated on the solution [Figure 1C]. In 1 h, the