Controlled Doping of Electrocatalysts through Engineering Impurities

Abstract

Fuel cells recombine water from H2 and O2 thereby can power, for example, cars or houses with no direct carbon emission. In anion‐exchange membrane fuel cells (AEMFCs), to reach high power densities, operating at high pH is an alternative to using large volumes of noble metals catalysts at the cathode, where the oxygen‐reduction reaction occurs. However, the sluggish kinetics of the hydrogen‐oxidation reaction (HOR) hinders upscaling despite promising catalysts. Here, the authors observe an unexpected ingress of B into Pd nanocatalysts synthesized by wet‐chemistry, gaining control over this B‐doping, and report on its influence on the HOR activity in alkaline conditions. They rationalize their findings using ab initio calculations of both H‐ and OH‐adsorption on B‐doped Pd. Using this “impurity engineering” approach, they thus design Pt‐free catalysts as required in electrochemical energy conversion devices, for example, next generations of AEMFCs, that satisfy the economic and environmental constraints, that is, reasonable operating costs and long‐term stability, to enable the “hydrogen economy.”

Boron-Doped Platinum-Group Metals in Electrocatalysis: A Perspective

“…37 Lowering the reaction temperature, increasing the mole ratio of DMAB or NaBH 4 to a Pd(II) precursor, and extending the reaction time favor an increased B-doping level. 37,47,57,58 In fact, under otherwise similar conditions, DMAB and NaBH 4 yield B-doping levels of ∼6.7 and 2.7 atom % in Pd nanoparticles, respectively, in aqueous-phase synthesis. 37 In addition, by adding an amphiphilic surfactant template, this aqueous synthesis involving DMAB can be further extended to construct different nanostructured Pd−B alloys such as nanospheres, nanowires, nanopillars, and so on.…”

“…B atoms could gradually diffuse into the Pd–Pd lattice in this DMAB reduction process, leading to an average B content ranging from 6.0 to 17.0 atom % in the reported Pd–B catalysts. ,, DMAB appears to be more effective in doping B for the aqueous-phase synthesis of PGM-B catalysts . Lowering the reaction temperature, increasing the mole ratio of DMAB or NaBH 4 to a Pd­(II) precursor, and extending the reaction time favor an increased B-doping level. ,,, In fact, under otherwise similar conditions, DMAB and NaBH 4 yield B-doping levels of ∼6.7 and 2.7 atom % in Pd nanoparticles, respectively, in aqueous-phase synthesis . In addition, by adding an amphiphilic surfactant template, this aqueous synthesis involving DMAB can be further extended to construct different nanostructured Pd–B alloys such as nanospheres, nanowires, nanopillars, and so on. ,,, …”

“…The absence of the typical β-hydride desorption peak from H 2 -temperature-programmed reduction further confirmed the incorporation of B atoms in Pd interstitial sites . Although electron energy loss spectroscopy (EELS) with a characteristic feature at 188 eV can be applied to characterize the elemental mapping of the B-dopant in a PGM, the 3D distribution of the B-dopant can only be obtained by using newly developed atom probe tomography (APT), nevertheless, this method has so far been limited to ∼100 nm particles …”

“…65 Although electron energy loss spectroscopy (EELS) with a characteristic feature at 188 eV can be applied to characterize the elemental mapping of the B-dopant in a PGM, 64 the 3D distribution of the B-dopant can only be obtained by using newly developed atom probe tomography (APT), nevertheless, this method has so far been limited to ∼100 nm particles. 57 It should be pointed out that most of the above physicochemical methods can also be very useful for characterizing the geometric structure changes in the B-doped PGM intermetallic, including but not limited to high angle annular dark field STEM, EELS mapping, HR-STEM, powder XRD, and APT, as demonstrated by Kitagawa et.al. 51 2.2.2.…”

“…(f) Calculations of H and OH binding energies for the HOR plotted as a function of the calculated ε d referenced to the Fermi energy. Reproduced with permission from ref . Copyright 2022 Wiley.…”