The objective of this proposal is to develop original and cheap photosensitive systems capable of generating a very strong reductive power upon illumination, which could be further used in various photochemical reactions or reduction catalysts activation. Reductive quenching (RQ) is particularly relevant within this frame: when a photosensitizer PS is promoted to its excited state PS*, it can be reductively quenched by a sacrificial donor: PS* + SD ? PS- + SD+. If PS is properly chosen such that E(PS/PS-) is very negative, strongly reductive species can thus be photo-generated. Heavy metal based complexes are very efficient in this area, but they are expensive and toxic. On the other hand, copper(I)-diimine complexes as PS (hereafter named PSCu) are elegant alternatives because they feature surprisingly similar photophysical properties than e.g. ruthenium complexes and substantially more cathodic reduction potentials than any heavy metal based PS, at much lower price and toxicity. Nevertheless, copper(I)-diimine complexes have almost never been used for RQ, despite these advantages. The reason is PSCu are weak photo-oxidants in general: the initial photo-induced charge separation PS* + SD -> PS- + SD+ is not thermodynamically feasible with usual SD. The aim of the PERCO project is to adjust the electronic properties of SD and PSCu for efficient RQ, via molecular engineering of both protagonists. The driving force for RQ is related to the equation E(PSCu/PSCu-) + E00 – E(SD+/SD), where E00 is the energy of the excited state of PSCu. Setting as an upper limit E(SD+/SD) = 0.3 V vs. SCE (criterion 1), and as a lower limit E(PSCu/PSCu-) + E00 = 0.6 V vs. SCE, a minimum driving force of 300 meV is insured for RQ. New SD will be obtained by modifying pre-existing well-known SD with electron donating groups. In parallel, new PSCu will be designed such that E(PSCu/PSCu-) + E00 is more positive (no less than 0.6 V vs. SCE). This will be achieved by modifying the pi-accepting properties of ligands coordinating copper(I) and tuning the steric bulk of the latter coordination cage, altering respectively E(PSCu/PSCu-) and E00. Very importantly, we will pay special attention not to annihilate the remarkably reductive power of PSCu- nor its light harvesting efficiency during chemical engineering, by imposing 3 additional criteria: 2) E(PSCu/PSCu-) must remain below -1.6 V vs. SCE, and 3) E00 must lie below 2.5 eV to insure visible light sensitivity. At last, the excited state lifetime of obtained PSCu must be long lived enough (ca. 70 ns) to insure the efficacy of bimolecular RQ reaction (criterion 4). With all gathered information, we will isolate homo- and heteroleptic copper(I) complexes able to perform RQ with pre-existing or newly synthesized SD. In particular, we will append anchors on the diimine fragment to allow chemisorption on a p type semi-conductor (e.g.NiO). We will study the photo-induced hole transfer from grafted PSCu into the valence band of NiO, en route towards photo-electrochemical cells. Finally, photo-active systems designed in this project will be put to the test in bulk photolysis experiments: we will monitor the photo-induced degradation of organic products featuring very negative reduction potential, in presence of PSCu and SD, or NiO|PSCu hybrid systems. All compounds will be characterized by electrochemistry and steady-state spectroscopies, in order to interpret and quantify the behaviour of our systems. Ultrafast spectroscopy (optical and X-ray) will be performed to appraise the intricate photo-induced processes at stake. The success of the PERCO project is relying on a collaboration between CEISAM (Nantes) and the Chen group (Northwestern University), who is specialised in the photophysical behaviour of copper based photosensitizers. The successful achievements of this proposal will pave the way towards cheap, fully renewable artificial photosystems for H2O or CO2 photocatalytic reduction.

Cities in the Global North are increasingly adopting nature-centered and other green infrastructure interventions to respond to climate risks and impacts and enhance their adaptation and resilience capacity. Yet, plans for such green infrastructure (GI) and other urban greening interventions tend to underestimate risks of displacement for lower-income and minority residents – what myself and others have previously called green climate gentrification. Despite increasing recognition of this process and concerns for the displaced, few municipal green interventions are coupled with social provisions (such as social housing; resident-driven economic development schemes) to protect residents from displacement. Yet, predicting and preventing green gentrification is the only way to build a green resilience agenda that upholds the stated social and environmental goals of such plans and avoid green paradoxes born out of urban renaturing projects and which municipalities have expressed commitment to avoid. In this POC, I propose to further analyze the social equity impacts of climate adaptation and green resilience efforts and build on my GreenLULUs ERC in order to (a) create a replicable, interactive community- and policy-driven predictor index, tool, and analysis for green gentrification in the context of planned green climate-centered infrastructure and (b) test the early development of an actionable, pilot municipal policy and planning instrument, such as a climate-adaptation focused community land trust, a municipal green bond program for equitable climate resilience, a community-based stewardship fund, or green minority-owned green business seed grants (among others) to prevent green climate gentrification. These tasks will be decided and built in partnership with municipal governments and community groups based on pilot cities included in my finishing ERC project – Barcelona and Boston – so that this POC can support them in their work for more just green cities.

CREATE aims at developing innovative membrane electrode assemblies for low-temperature polymer-electrolyte fuel cell (FC) and electrolyzer (EL) with much reduced cost. This will be achieved via elimination or drastic reduction of critical raw materials in their catalysts, in particular platinum group metals (PGM). Key issues with present low-temperature FC & EL are the high contents of PGM in devices based on proton-exchange-membrane (PEM) and the need for liquid electrolytes in alkaline FC and EL. To overcome this, we will shift from PEM-based cells to 1) pure anion-conducting polymer-electrolytes and 2) to bipolar-membrane polymer electrolytes. The latter comprises anion and proton conducting ionomers and a junction. Bipolar membranes allow adapting the pH at each electrode, thereby opening the door to improved performance or PGM-free catalysts. Both strategies carry the potentiality to eliminate or drastically reduce the need for PGM while maintaining the advantages of PEM-based devices. In strategy 1, novel anion-exchange ionomers and membranes will be developed and interfaced with catalysts based on Earth-abundant metal oxides or metal-carbon composites for the oxygen reactions, and with ultralow PGM or PGM-free catalysts for the hydrogen reactions. In strategy 2, novel bipolar membrane designs, or designs unexplored for FC & EL, will be developed and interfaced with catalysts for the oxygen reactions (high pH side of the bipolar membrane) and with catalysts for the hydrogen reactions (low pH side). The ionomers and oxygen reaction catalysts developed in strategy 1 will be equally useful for strategy 2, while identified PGM-free and ultralow-PGM catalysts will be implemented for the hydrogen reactions on the acidic side. Polymer-electrolyte FC & EL based on those concepts will be evaluated for targeted applications, i.e. photovoltaic electricity storage, off-grid back-up power and H2 production. The targeted market is distributed small-scale systems.