Structure Design And Formic Acid Oxidation Electrocatalytic Performances Of Platinum-Group Ordered Intermetallics

The higher theoretical voltage,energy density and lower fuel permeability render direct formic acid fuel cell（DFAFC）as one of the promising power installations.However,the anodic formic acid oxidation reaction（FAOR）mechanism remains complicated.And FAOR performances tend to be degraded when it is proceeded via an indirect pathway,as the catalysts are poisoned by the adsorbed carbon monoxide intermediates（CO*）.Therefore,promoting the FAOR selectivity and activity for direct production of carbon dioxide（CO₂）is key to the development of DFAFC by developing highly efficient electrocatalysts.In this paper,atomically ordered Pt-group intermetallics are constructed to reduce the poisoning of CO*by limiting the continuous active sites.Further,the structure-activity relationship for FAOR via the direct pathway is established by analyzing the influences of adsorbed hydroxyl（OH*）on the catalytic performances of intermetallics.At last,achieving the highly active and stable FAOR electrocatalysts by tailoring the adsorption properties of intermetallics.The main research contents and results are shown in the following.（1）Exploring the mechanism for limiting CO*formation on intermetallics.Constructing Pd-Bi ordered intermetallics（O-Pd Bi）to limit the formation of CO*during FAOR and promote the electrocatalytic performances.Due to the ordered atomic distribution on O-Pd Bi surface,Pd atoms are isolated by Bi atoms.When catalyzing FAOR,O-Pd Bi exhibits 1.9 and 5.3 times of promotion in specific activity than disordered Pd Bi alloy and pure Pd respectively.And the stability is greatly enhanced on O-Pd Bi as the current attenuation rate of O-Pd Bi is 2 orders of magnitudes smaller than that of pure Pd at 0.35 V.In situ infrared（IR）spectra show that CO*is involved in the FAOR process on pure Pd,but CO*is suppressed on O-Pd Bi electrode,resulting in decreased CO*poisoning.（2）Constructing the structure-activity relationship between the catalytic performances and surface OH*adsorption energy on intermetallics.Ternary Ir-based ordered intermetallics are prepared when partial Ir atoms are replaced by Pd atoms,the OH*adsorption strength on which is decreased than binary Ir₃V intermetallics and pure Ir,leading to 2.3 and 7.3 times of promotion in electrocatalytic mass activity for FAOR respectively.Further,Pt atoms are introduced into Rh Fe ordered intermetallics to avoid the excessive binding of OH*,which leads to 2.6 times of promotion in FAOR mass activity than Rh Fe.As FAOR activities of multiple intermetallics are related to OH*adsorption energy,OH*is confirmed to be a descriptor for the FAOR activity.（3）Stabilizing the surface OH*adsorption energy on intermetallics.Multi-elemental Pt-based ordered intermetallics O-（Pt Pd Ir Ru）₂Fe Cu are constructed to promote catalytic stability.Electrochemical tests show that O-（Pt Pd Ir Ru）₂Fe Cu delivers about 3 times of promotion in mass activity than O-Pt₂Fe Cu as well as greatly improved stability.O-（Pt Pd Ir Ru）₂Fe Cu shows no loss in activity after potential cycling for 1 200 cycles due to the stable adsorption of OH*on surface,while O-Pt₂Fe Cu suffers a loss in activity at about 40%.Ir and Ru are mainly responsible for stabilizing the OH*adsorption on multi-elemental Pt-based ordered intermetallics while Pd is easy to be corroded.Hence,increasing anti-corrosion elements in intermetallics is key to stabilizing OH*adsorption properties.（4）Optimizing the OH*adsorption energy of electrocatalysts for achieving a higher atomic utilization.Au Cu intermetallics supported Pt single-atom electrocatalysts are constructed for further promoting FAOR activity and stability.The Cu atoms on the surface of Au Cu intermetallics are replaced by Pt atoms via a spontaneous replacement strategy.By selecting the Pt salts with different valence states,catalysts with atomically dispersed Pt（Pt₁-Au Cu）and Pt clusters（Pt_n-Au Cu）are obtained.Pt₁-Au Cu displays 2.0and 95.5 times of promotion in mass activity than Pt_n-Au Cu and pure Pt respectively,due to the optimized OH*adsorption property.Benefited by the anti-corrosion property of Au,FAOR proceeds via the direct pathway on Pt₁-Au Cu after potential cycling.Thus,FAOR activity and stability are optimized synchronously by employing intermetallics tailored single-atom electrocatalysts.