Tuning the compositions and structures of Pdbased nanomaterials and their supports has shown great potentials in facilitating the sluggish ethanol oxidation reaction (EOR) in alkaline direct ethanol fuel cells. Accordingly, a facile solvothermal method involving Cu and Pd composition migrations is developed in this study, to synthesize highly uniform and small-sized nanospheres (NSs) possessing the special structures of composition-graded (CG) Cu 1 Pd 1 and surface-doped (SD) Ir 0.03 , which are evenly anchored onto N-doped porous graphene (NPG) as a highperformance EOR electrocatalyst ( CG Cu 1 Pd 1 / SD Ir 0.03 NSs/ NPG). Comprehensive physicochemical characterizations, electrochemical analyses, and first-principles calculations reveal that, benefiting from the NPG-imparted mass-transfer and oxygen-reduction effects, the CG−SD structural and sizemorphology effects of the NS, as well as the Cu-and Ir-induced bifunctional, geometric, and ligand effects, CG Cu 1 Pd 1 / SD Ir 0.03 NSs/NPG exhibits not only ultrahigh electrocatalytic activity and highly efficient noble-metal (NM) utilization, showing 7105 and 6685 mA mg −1 in Pd-and NM-mass-specific activity (MSA), respectively, which are 15.8 and 14.9 times those of commercial Pd/C, but also satisfactory electrocatalytic durability, retaining respective 28.1-and 19.2-fold enhancements in Pd-MSA compared to the commercial Pd/C, after 1 h chronoamperometric and 500-cycle potential cycling degradation tests. This study not only provides an effective and versatile synthetic strategy to prepare the NM-efficient metal-based nanomaterials with the special CG and SD structures for various electrocatalytic and energy-conversion applications, but also proposes some insights into the composition-and structure-function relations in EOR electrocatalytic mechanism for rationally designing highly active and durable EOR electrocatalysts.

High-loaded oxygen reduction reaction (ORR) Pt intermetallic compounds with high performance expression under PEMFC operating conditions are prerequisite for practical application. Nevertheless, high metal-loading would lead to the severe agglomeration...

Summary Green synthesis of ammonia by electrochemical nitrogen reduction reaction (NRR) shows great potential as an alternative to the Haber-Bosch process but is hampered by sluggish production rate and low Faradaic efficiency. Recently, lithium-mediated electrochemical NRR has received renewed attention due to its reproducibility. However, further improvement of the system is restricted by limited recognition of its mechanism. Herein, we demonstrate that lithium-mediated NRR began with electrochemical deposition of lithium, followed by two chemical processes of dinitrogen splitting and protonation to ammonia. Furthermore, we quantified the extent to which the freshly deposited active lithium lost its activity toward NRR due to a parasitic reaction between lithium and electrolyte. A high ammonia yield of 0.410 ± 0.038 μg s −1 cm −2 geo and Faradaic efficiency of 39.5 ± 1.7% were achieved at 20 mA cm −2 geo and 10 mA cm −2 geo, respectively, which can be attributed to fresher lithium obtained at high current density.

Electrochemical oxygen reduction could proceed via either 4e−-pathway toward maximum chemical-to-electric energy conversion or 2e−-pathway toward onsite H2O2 production. Bulk Pt catalysts are known as the best monometallic materials catalyzing O2-to-H2O conversion, however, controversies on the reduction product selectivity are noted for atomic dispersed Pt catalysts. Here, we prepare a series of carbon supported Pt single atom catalyst with varied neighboring dopants and Pt site densities to investigate the local coordination environment effect on branching oxygen reduction pathway. Manipulation of 2e− or 4e− reduction pathways is demonstrated through modification of the Pt coordination environment from Pt-C to Pt-N-C and Pt-S-C, giving rise to a controlled H2O2 selectivity from 23.3% to 81.4% and a turnover frequency ratio of H2O2/H2O from 0.30 to 2.67 at 0.4 V versus reversible hydrogen electrode. Energetic analysis suggests both 2e− and 4e− pathways share a common intermediate of *OOH, Pt-C motif favors its dissociative reduction while Pt-S and Pt-N motifs prefer its direct protonation into H2O2. By taking the Pt-N-C catalyst as a stereotype, we further demonstrate that the maximum H2O2 selectivity can be manipulated from 70 to 20% with increasing Pt site density, providing hints for regulating the stepwise oxygen reduction in different application scenarios.

Oxygen reduction reaction (ORR) plays a critical role in various renewable energy technologies, however, the unsatisfactory ORR electrocatalytic performance of commonly used commercial electrocatalysts under alkaline and acidic conditions greatly...

In the past few years, great progress has been made in nonprecious metal catalysts, which hold the potential as alternative materials to replace platinum in proton exchange membrane fuel cells. One type of nonprecious metal catalyst, Fe− N−C, has displayed similar catalytic activity as platinum in rotating disk electrode tests; however, rapid degradation of Fe−N−C catalyst-based fuel cells is always observed, which limits its practical application. Although considerable research has been devoted to study the degradation of the catalyst itself, rather less attention has been paid to the membrane electrode assembly that makes the mechanism of fuel cell degradation remain unclear. In this work, a high-performance Fe−N−C catalyst-based membrane electrolyte assembly is prepared and used to study its degradation mechanism. The fuel cell performs with an initial peak power density as high as 1.1 W cm −2 but suffers a current loss of 52% at 0.4 V over 20 h only. The experimental and DFT calculation results indicate that Fe at active sites of catalysts is attacked by hydroxyl free radicals decomposed from H 2 O 2 , which is further leached out, causing an increase in activity loss. The ionomer of the catalyst layer and the membrane is further contaminated by the leached Fe ions, which results in an enlarged membrane resistance and cathode catalyst layer proton conduction resistance, greatly influencing the cell performance. In addition, it has been assumed in previous studies that the quick performance loss of Fe−N−C-based fuel cells is caused by water flooding within the catalyst layer, which is proved to be incorrect in our study through a dry-out experiment.

Rationally engineering the surface physicochemical properties of nanomaterials can improve their activity and durability for various electrocatalytic and energy conversion applications. Cu–Pd/Ir (CPI) nanospheres (NSs) anchored on N-doped porous graphene (NPG) [(CPI NSs/NPG)] have been recently demonstrated as a promising electrocatalyst for the alkaline ethanol oxidation reaction (EOR); to further enhance their electrocatalytic performance, the NPG-supported CPI NSs are coated with Au submonolayer (SML) shells (SMSs), through which their surface physicochemical properties can be tuned. CPI NSs/NPG is prepared by our previously developed method and possesses the special structures of composition-graded Cu1Pd1 and surface-doped Ir0.03. The Au SMSs with designed surface coverages are formed via an electrochemical technology involving incomplete Cu underpotential deposition (UPD) and Au3+ galvanic replacement. A distinctive volcano-type relation between the EOR electrocatalytic activity and the Au-SMS surface coverage for CPI@AuSML NSs/NPG is revealed, and the optimal CPI@Au1/6ML NSs/NPG greatly surpasses commercial Pd/C and CPI NSs/NPG in electrocatalytic activity and noble metal utilization. More importantly, its electrocatalytic durability in 1 h chronoamperometric and 500-cycle potential cycling degradation tests is also significantly improved. According to detailed physicochemical characterizations, electrochemical analyses, and density functional theory calculations, the promoting effects of the Au SMS for enhancing the EOR electrocatalytic activity and durability of CPI NSs/NPG can be mainly attributed to the greatly weakened carbonaceous intermediate bonding and properly increased surface oxidation potential. This work also proposes a versatile and effective strategy to tune the surface physicochemical properties of metal-based nanomaterials via incomplete UPD and metal-cation galvanic replacement for advancing their electrocatalytic and energy conversion performance.

Proton exchange membrane water electrolysis (PEMWE) is a key technology to solve the serious energy and environmental problems. However, the poor durability of electrocatalysts in acidic oxygen evolution reaction (OER) environment hinders the large-scale application of PEMWE. Herein, a robust RuMn electrochemical catalyst with a remarkable durability within 20 000 cyclic voltammetry cycles is reported. Furthermore, RuMn is stable for 720 h at 10 mA cm -2 current density in 0.5 M H 2 SO 4 solution with <100 mV overpotential increase, outperforming the most electrocatalysts reported to date, by far. An amorphous RuO x shell is detected after the OER test, indicating a surface reconstruction process on the catalyst that inhibits steady-state dissolution. Further study demonstrates that the excellent durability of RuMn realized by protective RuO x can be attributed to strong bond strength of Ru, which is supported by density functional theory calculations with high dissolution voltage. Thus, improving the bond strength of Ru extends the design strategy for the Ru-based alloy catalysts with considerable stability.