Harnessing hydrogen spillover: Biomimetic dual-site platinum-gold catalyst mimicking NAD+ -reducing hydrogenase

Hydrogenases, nature’s extremely environment friendly biocatalysts for the interconversion of H₂ and H⁺, have garnered vital consideration [1], [2]. Among the many varied courses of hydrogenases, the soluble NAD⁺-reducing hydrogenases (SH) are significantly noteworthy—not just for their essential function in H₂/H⁺ conversion but additionally for his or her distinctive potential to mediate the interconversion of the high-value cofactors NAD⁺ (nicotinamide adenine dinucleotide) and NADH [3], [4], [5]. SH operate as an environment friendly catalyst for hydrogen oxidation (HOR), and when coupled with oxygen discount, permits the event of H₂/O₂ biofuel cells [6], [7]. This method gives a extremely environment friendly and biocompatible platform, selling the sustainable and efficient utilization of unpolluted vitality. Past their function in HOR, SH can selectively scale back NAD⁺ to 1,4-NADH, a key electron switch mediator and vitality service important for mobile metabolism and a variety of redox reactions [8], [9]. Environment friendly regeneration and sustainable recycling of 1,4-NADH are essential for enhancing the longevity and financial viability of catalytic methods. Thus, the twin functionalities of SH in HOR and selective NAD⁺ discount underscore the potential as a promising mannequin for designing biomimetic catalysts, paving the best way for developments in bioelectrocatalysis and biosynthetic methods.

Nevertheless, intrinsic fragility and restrictive working circumstances, similar to deactivation at excessive potential, hampered their additional growth and utility [10], [11]. Designing rational and environment friendly hydrogenases-like catalysts and broadening their functions are indispensable however stay challenges. Efforts to deal with these challenges usually contain the event of artificial iron- and/or nickel-based molecular catalysts, impressed by the structural options of hydrogenase energetic facilities [12], [13], [14]. Regardless of these efforts, the complexity of those molecular catalysts poses vital obstacles, similar to difficult materials synthesis and difficulties in unraveling their catalytic mechanisms [13], [15]. Critically, present analysis on molecular hydrogenase mimics has been predominantly centered on modeling the NiFe energetic web site alone, which solely can obtain both hydrogen oxidation or evolution. So far, no biomimetic system has efficiently replicated the whole purposeful biomimicry of SH, as this could require simultaneous engineering of each the NiFe and the FMN websites. To deal with the problems of structural replication and fill a important analysis hole, an alternate strategy-developing catalysts by mimicking the catalytic processes/mechanisms of pure enzymes.

Via the proton-coupled electron switch (PCET) mechanism, the SH facilitates the coupling of two half-reactions: dehydrogenation oxidation and hydrogenation discount [4], [16], [17]. Each processes are facilitated by the SH’s two distinct energetic websites individually: the NiFe and the FMN. On the NiFe web site, H₂ is dissociated into two protons and two electrons. These two electrons are subsequently transferred to the FMN web site through iron-sulfur (FeS) clusters, the place they recombine with a proton to kind a hydride intermediate, finally decreasing NAD⁺ to NADH. The PCET mechanism in enzymatic catalysis intently parallels the hydrogen spillover mechanism generally noticed in chemical catalysis, significantly in binary composites, the place energetic hydrogen (H_act) species migrate from one web site dissociating H₂ to a different web site for subsequent reactions [18], [19]. This mirrors the operate of the NiFe/FMN web site in PCET mechanism, presenting the connection between organic and chemical catalytic processes [20]. Impressed by these catalytic mechanisms, mimicking the twin catalytic websites of SH, which concurrently facilitates hydrogen oxidation (HOR) and NAD⁺ discount, requires designing a catalyst with the next key traits: (1) two distinct elements serving as energetic websites with markedly completely different hydrogen adsorption properties, and (2) complementary catalytic actions, the place one element displays excessive effectivity for hydrogen activation and the opposite demonstrates sturdy catalytic efficiency for NAD⁺ discount. Platinum (Pt) is well-known for its distinctive catalytic exercise in HOR however falls brief in decreasing NAD⁺ [21], [22], [23], [24]. Conversely, gold (Au) exhibits a robust affinity for NAD⁺ hydrogenation however lacks exercise for HOR [25], [26]. Given these complementary properties, we hypothesized that alloying Pt with Au may create a synergistic system, successfully mimicking the catalytic habits of SH by means of hydrogen spillover mechanism.

On this research, we synthesized biomimetic platinum-gold (PtAu) catalyst, as a theoretical mannequin, to breed the capabilities of SH, reaching HOR and NAD⁺ discount in biocatalysis and electrocatalysis. Right here, Pt and Au have been employed to imitate the NiFe and FMN energetic websites, respectively, with hydrogen spillover mechanism changing the PCET mechanism of SH. Theoretical calculations and experimental outcomes revealed the person contribution and synergistic interactions between Pt and Au, validating the hydrogen spillover catalytic mechanism and demonstrating the effectiveness of this mechanism-inspired technique. Theoretically, molecular docking evaluation confirmed the catalytic mechanism of SH, whereas density purposeful principle (DFT) calculations quantified adsorption interactions between Pt/Au and H₂/NAD⁺, in addition to validated the feasibility of hydrogen spillover course of. Experimentally, complete outcomes of colorimetric technique, complemented by chemical inhibition experiments, revealed the distinct roles and synergistic interactions between Pt and Au websites. The hydrogen spillover phenomenon was additional confirmed utilizing electron paramagnetic resonance (EPR) spectroscopy and nuclear magnetic resonance (NMR). Consequently, the catalytic course of on PtAu catalyst might be speculated: Pt websites dissociated H₂ to provide H_act, which subsequently migrated to adjoining Au websites to facilitate the NAD⁺ hydrogenation.

In biosynthesis, PtAu catalyst achieved a outstanding 100 % conversion of NAD⁺ with 72 % selectivity for 1,4-NADH, considerably outperforming beforehand reported Pt-based catalysts and industrial Pt/C (20 %). Theoretical calculations revealed that PtAu considerably enhanced the NAD⁺ adsorption whereas concurrently selling the H_act desorption, contributing to their superior efficiency. Much like SH, PtAu catalyst may switch electrons to varied acceptors, together with NAD⁺, flavin adenine dinucleotide (FAD), and flavin mononucleotide (FMN), and cascade with pure enzymes for high-value chemical substances synthesis. In bioelectrocatalysis, past its capability to electrocatalyze the discount of NAD⁺ to 1,4-NADH, PtAu catalyst additionally successfully facilitated the electrocatalytic HOR. Integrating PtAu catalyst (anode catalysts) with bilirubin oxidase (cathode catalysts), we constructed a H₂/O₂ enzymatic biofuel cell (EBFC) working below ambient temperature, strain, and impartial pH circumstances. The EBFC achieved a formidable energy output exceeding 2.0 mW cm⁻² and exhibited outstanding operational stability, with solely a 4 % decline in energy output after 50 h of steady operation. This research underscored the potential of using biomimetic catalytic mechanisms for rational design, and broadening functions of catalysts in bioelectrocatalysis and biosynthesis methods.